By the 19th-20th centuries, Britain had basically stripped Ireland of many of its natural resources. I'd wager that any of you picture rolling green hills when you hear the name "Ireland", but pre-modern Ireland was in fact covered in dense, old-growth forest that was cut down to fuel industrialization, supply early modern Britain's insatiable demand for ship timber, and because of goats (no, seriously). For British observers, Irish timber was the only really significant resource to be found on the island; the earliest colonial maps and surveys frequently comment on the massive size and sturdiness of Irish trees and their potential utility for the British navy. Besides that, there were no significant mineral deposits (contrary to an above post which claims that Ireland had large coal mines) or exotic materials, unless you count lots and lots of peat. Even in the context of agriculture, only the province of Munster and the central plateau of Mide were really suited for growing wheat on a large scale.

So why did Britain hold on to Ireland so tenaciously if it lacked any real resources? As others have mentioned, it had manpower, a strategic location for both Britain's role as a global naval power and as a potential launching pad for an enemy invasion (which the English rightly feared; Irish lords had called upon the Hapsburg king of Spain to send troops during the 9 Years' War, and the revolutionary Wolfe Tone arrived in Ireland with over 1000 French soldiers during the rebellion of 1798 and medieval Irish history is rife with rebellions beginning in Ireland and spreading to England).

Something that no one has really addressed so far was the ideology that motivated continued British domination of the island. By the 19th century, many Britons, especially those of higher classes, had developed a very racialized and derogatory perception of the Irish character. A perfect example can be found in John Horace Round's 1899 writings on the British conquest of Ireland in The Commune of London, and other studies:

In Ireland, on the contrary, the new comers found no kindred system.Its tribal polity had placed between its people and themselves a gulf impassable because dividing two wholly different stages of civiliza- tion. With no common foundation on which to build, they could only hope to become Irish by cutting them- selves off from their own people.

He then wonders "whether Ireland, if left to herself (in 1899!!), would even yet have emerged from the tribal stage of society becomes doubtful when we contemplate the persistence of the mores Hibernici." He then goes full on imperialist in the following diatribe:

We went to Ireland because her people were engaged in cutting one another's throats ; we are there now because, if we left, they would all be breaking one another's heads... Claiming to govern a people when they cannot even govern themselves, they clamour like the baboo of Bengal against that pax Britannica by the presence of which alone they are preserved from mutual destruction. No doubt, as one of them frankly confessed, they would rather be governed badly by themselves than well by any one else. But England also has a voice in the matter ; and she cannot allow the creation of a Pandemonium at her doors.

This was the main ideological motivation behind calls for a continued British imperial presence in Ireland. Many if not most of Britain's elite viewed the Irish as a lesser race, prone to violence and possessing a low intelligence and incapable of maintaining any kind of civilization without the guiding and benevolent hand of the Anglo-Saxon race. The fact that Ireland was also right next to Britain made outright independence a terrifying thought. Because they viewed the Irish as a lesser race held under the benevolent Pax Britannica of the British Empire, Ireland's independence was doubly fearful because of the potential it had to upset the rest of Britain's global empire: just as Round compared the Irishman to the "baboo of Bengal", so too did many British officials fear that Irish independence, or even devolved parliament (which was actually the only thing Irish nationalists were advocating for, outright independence was only the goal of a small percentage of militant nationalists) would lead to the collapse of the British empire as colonial subjects in India, Africa and Asia might take Ireland's example and demand more independence. This had some factual merit as Indian and Irish independence leagues and figureheads were supposedly in touch with each other at the beginning of the 20th century, especially after the Irish revolt of 1916.

I think you're ignoring the fact that many wealthy English people owned land in Ireland. It wasn't just an imperative to keep it politically. People owned big chunks of it and didn't want their taxes, labour conditions, etc. changed by a new independent government.

Ireland has one very important natural resource that nobody else seems to have mentioned yet: people.

For starters, there were a lot of generals and admirals of Irish descent in the British Empire. The most famous example would be Wellington, perhaps, but Wellington absolutely did not consider himself Irish -- the fact that he was born in Dublin was a fluke of geography. Despite that (and a fairly cosmopolitan upbringing), Wellington's father and grandfather were very clearly Irish. His father even served in the Irish House of Commons (for, near as I can tell, only a short term). His maternal grandfather, also an Irishman, served in the Irish House of Commons before being elevated to the Irish House of Lords. Wellington may not have considered himself Irish, and he was almost certainly from a Protestant family, but he was very much a product of Ireland. Wellington also had a number of successful relatives, too.

Kitchener is another example. He made his name fighting Britain's colonial wars (first Sudan, then the Boers), but he earned his fame from fighting in WWI. Kitchener is one of the better remembered British generals (although perhaps not as much so as the amusingly named John French). He was killed when his ship struck a German mine in Scottish waters. Kitchener was born in Ireland, some time after his father had purchased land there after selling his commission (I'm not sure where his father was born, but his grandfather was born in England, but considering his mother was also from England, I'd guess that his father was from there, too). His family was very much another of those Anglo-Irish families.

A more cut-and-dry example might be Admiral of the Fleet Callaghan, who was born to an Irish landowner and went on to serve in the Boxer Rebellion and WWI. Callaghan commanded the Home Fleet at the outbreak of the war, but he was sacked and replaced by Jellicoe in a fairly unprecedented example of Churchill's meddling in WWI (this turned public opinion against him, and apparently even Jellicoe was outraged despite getting a promotion over it, and probably didn't help Churchill's career when Gallipoli failed).

You get the idea. There were a bunch of high-ranking Irishmen in the British military. Perhaps not as many as the generals and admirals of Scottish descent (seriously, it seems like Scotland produced way more officers than it had any right to given its size), but still a fair few. And then there's the regular manpower contribution.

In fact, there are claims that 42% of all enlisted personnel in the British Army were Irish, but I haven't actually reviewed the source material for that claim. Regardless of whether or not the specific number is true, the intention is clear: there were a lot of Irishmen who fought and died for the United Kingdom.

Which period are you referring to? If you mean the 19C and 20C rebellions, consider that an analogous question would be "Why did the state of New York hold on to the Southern States so stubbornly?". At the period in question, both England and Ireland were constituent countries of the United Kingdom, with representation in Parliament. Ireland was not viewed as an external part of the Empire like India or Australia, hence was never seen as having a right to separate.

There is a danger of presentism - looking at the current borders of a country and assuming that previous administrations were incorrect in trying to hold previous borders. But consider - should Alsace-Lorraine belong to France or Germany? Should Texas and New Mexico belong to the USA or to Mexico?

For the end of the 19th century into the 20th the Irish independence movement was different from previous autonomy efforts. In this period it was motivated by ideologies of nationalism and self-determination rather than inter-feudal competition. One of the main reasons why the British government was so intransigent against giving Irish independence was the fear that this would lead to a string of independence movements across the empire. If England lost Ireland in it's own backyard this would lead to great inspiration among the rest of the British colonies.

A good reference book on this debate is Imperialism: The Robinson and Gallagher Controversy

Haven't seen this mentioned but thought I read once it was strategic (edit has been mentioned), due to England being at conflict with Catholic countries (on the Pope's approval) and Ireland could have been used by those countries to launch invasions.

BBC has a good background on past invasions which may shed more light.

I believe it started with the Normans after they helped an ousted king get his throne back and they cemented their nobles there. England had wars with France for the same reason, nobles and kings who saw it as their right to own land their ancestors won and those trying to win it back from them or have claimed it themselves since. King see's it as his right and doesn't want to seem weak to lose it, also lower nobles want it too and king has to keep them happy. Money, food, people for armies can come from castles and land.

Just as in Scotland a century later, the trouble with the English began with a civil war among the natives. In 1166, the King of Leinster, Diarmait MacMurchada was forced to flee from Dublin and from his kingdom by an alliance of Irish enemies, including the new High King, Ruaidri Ua Conchobair. 'Awful the deed done in Ireland today', wrote the chronicler of Leinster, 'the expulsion overseas by the men of Ireland of Diarmait...'.

And awful were its consequences. For Diarmait landed in Bristol and asked for help from King Henry II to get his throne back. Now what happens when you ask the Godfather for a favour? He expects something, some day, in return. And, as the Song of Dermot made clear, from the beginning that something was:

To you I come to make my plaint, good sire In the presence of the barons of your empire. Your liege-man I shall become henceforth all the days of my life, On condition you be my helper so that I do not lose at all You I shall acknowledge as sire and lord...

Then the King promised him, the powerful king of England That willingly would he help him as soon as he should be able.

This is when the trouble became big trouble. For Diarmait promptly went shopping for mercenaries among the nastiest and greediest possible bunch of knights. These were the Anglo-Normans who, around the 1160s, seemed to be on the losing end of the war against the Welsh princes of Gwynedd.

They had lost castles, land and peasants. They were in an ugly mood and they were looking for somewhere to recoup their losses. Enter Diarmait.

Spread the word, the likes of Robert fitzStephen and Richard fitzGilbert de Clare (known to his friends, and especially to his many enemies, as 'Strongbow') must have said: 'Forget about Wales; forget about those unpleasantnesses in the mountains and valleys. Come west young knights. Ireland will be a piece of cake. It's said that the natives are primitive. But the pastures are green. So what are you waiting for?'.

Within a year Diarmait had his throne back in Dublin. But he also now had an army of Anglo-Normans who weren't about to go away now that the job was done. In fact, from the beginning, Diarmait had known this. He not only expected but wanted the likes of Strongbow to stick around, lest his old enemies get ideas of booting him out again.

....

The devastating wars of the British nations, which had seen Edward I invade Wales and then Scotland in the 13th century, left Ireland largely unaffected.

However, Edward, the Caesar of Britain, had inherited the English Crown's claim to be Lord of Ireland, along with the rest of his estates. Irish gold contributed to his campaigns in Wales, 3,000 Irish men invaded Scotland with him, and while Irish grain fed his war machine, Edward never visited the island himself; indeed no English king did so between John and Richard II.

Significantly, and for the first time, the grant of Ireland to Edward: 'provided that the land of Ireland shall never be separated from the crown of England...', and so left it forever a part of the Plantagenet estate.

Anglo-Norman lords had settled in Ireland in the 12th century and never left. Its landscape now featured Norman castles and abbeys, just like the British mainland.

...

And then in May 1315, Bruce did something much, much, bolder. His brother, Edward, landed a formidable Scottish army, at least 5,000 strong, near Carrickfergus in the north-east of Ireland. In effect, this opened a second front in the war against the English empire.

The Scots would come, he said, not as invaders but as liberators, for: 'our people and your people, free in times past, share the same national ancestry and are urged to come together more eagerly and joyfully in friendship by a common language and common custom'.

What he was proposing was a Gaelic alliance, across the Irish Sea, 'so that God willing, nostra natio - our nation - may be restored to her former liberty'.

Let's take this question theme by theme. Firstly however let me reverse the question 'Why would the British have let Ireland have independence?' Britain had dominated Ireland from the sixteenth century onwards. Major powers don't just let regions go; France didn't just walk away from Normandy or Burgundy and the USA fought a civil war to retain the south. The idea that small nations had a right to self-determination is pretty modern.

A note on terminology, historians don't use England or the English after the Union with Scotland of 1707. We use Britain and try to avoid "the British" unless we are actually talking about the whole people. After 1800 we use "the UK" for Britain and Ireland as a political entity and Britain for England, Scotland and Wales.

Theme 1: economics

Ireland has very few significant minerals and its coal production was irrelevant to British industrial development. Ireland's major industry was agriculture and its main export was food, especially beef. Therefore Britain needed Ireland most when it was engaged in war (for example, 1800-15 and 1914-18). One of the arguments for the Union of 1800 was that it would allow Ireland better access to British markets. Aside from agriculture, linen and shipbuilding in the North East of Ireland gave Britain a reason to want to retain control but also created substantial support for the Union at middle and working class level.

Aside from the macro economic argument, Ireland was closely connected to Britain at a private level. Until the early twentieth century the owners of Irish land also owned large estates in Britain. Many of these were also beneficiaries of industry, for example the Londonderrys. I have found some 200 members of the House of Lords with Irish interests and connections.

Theme 2:Security

There are two slightly paradoxical arguments here; on the one hand Ireland was enough of a potential security threats to require Britain to retain control, on the other it was less of a security headache than is often assumed and so control was not that difficult.

Ireland had posed a direct threat to British interests several times most prominently in its support for James II and in in the 1790s when French intervened half heartedly in the United Irishmen rebellion. No major state would create a potentially hostile neighbour unless it had to. Ireland also provided strategic ports.

On the other hand, Ireland was not especially difficult to retain. Although Irish nationalists have tried to rewrite history to claim that the Irish were in constant rebellion against British rule, the reality was that the administration in Dublin Castle handled most of these fairly easily. The 1798 rebellion, the 1916 Rising and the revolution of 1919-21 did require significant military resources but other heroic failures such as the rebellions of Robert Emmet or the Young Irelanders did not. The biggest agitation surrounded demands around how Ireland was governed such as Catholic rights, land reforms and Home Rule ( having a local devolved government akin to modern Scotland ). Therefore Ireland was important enough to keep and did not demand too many resources to control.

Theme 3: Imperialism and Nationalism

I have grouped these together as there is a long debate about whether Ireland was a Colony or a part of British domestic government. To paraphrase Thatcher, can we say Ireland was as British as Finchley or was it comparable to Kenya. The best treatment of this is by David Fitzpatrick in his The Two Irelands which points out that it was a mixture. Unlike a colony, Ireland was fully represented in Parliament had elections as democratic as their British counterparts. However it had a colonial style chief secretary with a seat at Cabinet. This points out a crucial problem with the Union; it never fully evolved into a true federal relationship between the four kingdoms. Britain was the product of English military and economic domination and it was never resolved whether the UK should be a massive unitary state like France or a multi ethnic empire like Austria-Hungary.

Ireland was closely intertwined with the British state from the Tudor period onwards. Disentangling it was not a simple matter and would have run counter to the historical development of British national identity as outlined particularly by Linda Colley in Britons. It would have had spin off effects on the Empire also if a precedent was established that national self determination was reason to leave. Even the much more moderate proposal of Home Rule split the British party system and brought Ireland to the brink of civil war.

This raises another aspect of this theme, the belief, however paternalistic, that Ireland was better off under British rule. It was a key element of British nationalism that Britain was a benevolent nation with a mission to spread civilisation. Ireland was clearly underdeveloped. Nationalists blamed the British for this but the British understanding was that it was caused by Catholicism, poor education and a lack of modern industry and technology. Much of British activity in Ireland after the Famine was designed to improve the country and bring it up to "civilised" standards. Hence the introduction of national schools, a university system, the disestablishment of the Church of Ireland and a radical programme of land reforms far more extensive than anything in Britain. Conservative Unionists believed that it was possible to convince Irish people to support the Union through such reform. Gladstone broke with this view in 1885 and accepted the Union had failed and that Ireland would need its local parliament but even he never considered independence.

Theme 4: The Irish

Although the issue of self government dominated Irish politics after the 1860s, the demands of Irish politicians and their increasingly representative electorate were not that radical. The central demand was for a parliament in Dublin, subordinate to the Imperial Parliament in London. Ireland would have no military, foreign policy or sovereignty. More radical nationalists like the republican Fenians disdain education democracy and could never turn the support they got at mass demonstrations into active members or votes. No avowedly republican party made an electoral breakthrough until 1918. Therefore Britain could legitimately argue that Ireland was looking for reform of the Union, not independence.

Allied to the paternalistic view I mentioned earlier was a clear racism among many British people that held that the Irish could never successfully run a country. This was visible in cartoons in Punch which you can find via Google quite easily. According to this view, the Irish were inherently violent, emotional and credulous and would destroy themselves without the discipline and civilisation Britain provided.

Theme 5:Northern Ireland

Why did Britain retain the north-east corner of Ireland when the rest became independent? Partition was the bastard child of the Irish question an answer to what to do with the 20%+ of the population loyal to the Union. By 1913 they were powerful, organised and armed. Furthermore they had the support of the Conservative party and sections of the army who warned that they would not coerce Unionists. By 1920 partition was the easiest way to neutralise this threat and allow British forces to focus on the rebellion in the south. Since then successive British governments have been stuck with Northern Ireland and tried to avoid dealing with it until the Troubles forced them to. Since 1949 (The Ireland Act ) British policy has been to accept the decision of the majority in Northern Ireland and this was accepted by the Irish later on.

Conclusion

The simple answer is that there was no reason for Britain to give up Ireland by contemporary standards. Allowing territories that you control to walk away was not how major powers behaved. Britain had much to lose from Irish independence and nothing to gain. Ireland was not especially difficult to hold though it was a challenge to govern it well. The really important question is how Irish nationalists were able to fashion such a powerful ideology and use it to change the terms of the debate.

It wasn't until Henry VIII that Ireland became so important to the English crown. Before that, the major towns were largely autonomous and ruled by anglo-irish lords. The only area that was truly under crown rule was "the pale" i.e Dublin and surrounding areas. Henry VIII declared himself King of Ireland to strengthen control, before getting rid of strong Anglo-irish Families, mainly the fitzgeralds. He realised that if he didn't strengthen English control over the Island he would risk leaving England vulnerable to another major European player (France, Spain...) especially at a time when he abandoned Rome.

source: I study History at University College Cork.

I would suggest that the basic question here is wrong, or at least wrongly phrased or worded. I'm not sure that there is any evidence to suggest that "the English" tried to hold on to Ireland "so stubbornly" at all. If one looks at what could be seen as attempts by Ireland to further an agenda of independence, the first attempt wasn't until 1798. The 1798 rising is often portrayed, especially by Irish nationalists as an expression of Irish nationalism and as an attempt to establish Irish independence. However, if one looks at the process and the progress of the rising it will become clear that the '98 was no such thing. Although Irish nationalism was expressed during the rising, it was by no means a universal sentiment. Many of the United Irishmen had risen for class-based political reasons, or for economic reasons. Some rose in support of their catholic religion, yet others, like Wolfe Tone, and those at Ballynahinch, led by Henry Munro were protestants. The 1798 could better be seen as an outbreak of Revolutionary activity, rather than a nationalist outbreak. A rebellion rather than an attempt at gaining independence. In any case, the fact that it wasn't monolithic in aims or structures argues against it being a viable attempt at gaining independence. Most of the population in most parts of Ireland were apathetic at best, and many Irish, both catholic and protestant, took the side of the existing regime. The subsequent political movements were all aimed at greater representation in Ireland's government rather than independence. The Home Rule movement, politically introduced, supported and furthered by the British government, was aimed in that way. Although Home Rule was opposed in Ireland by the protestant north, and by the protestant land owning class in the south, usually referred to as the "Protestant Ascendancy", and was opposed by the Tory Party in the rest of the UK for party political reasons, the concept was generally supported in Britain as well as in Ireland. This suggests that there was no serious attempt by Britain to "hold on to Ireland", stubbornly or otherwise. The nationalist movement, in terms of seeking independence, up to 1914, was very much a minority, made up partly of a number of romantics who wished to establish an independent Ireland that would be a rural idyll, like Patrick Pearse, and partly of radical men of the far left, like James Connolly. Without going too much into the details of the Easter Rising and the Civil War, I would argue that the main reason why Lloyd George (the British Prime Minister, who was Welsh) sought a settlement was that the British people were opposed to holding onto Ireland by force. The actions of the army and the Tans in Ireland were very unpopular amongst the general population, which again shows that the assertion that the "English" attempted to hold on to Ireland stubbornly, or even hold on to Ireland at all, is simply not true. Partition was to allow the protestants of the North a degree of self-determination, not as an attempt to "hold on to Ireland". http://www.schoolhistory.co.uk/forum/uploads/monthly_03_2007/post-5215-1175202511.jpg The cartoon here shows that Lloyd George's intention was for the North to merge with the South, in the end, leading to a unified and ultimately independent Ireland. There is simply no evidence to support the assertion.

This is more of a geopolitical question than a historical one. Why would any country want to hold on to a region? Because that's what the "jus gentium" calls for. If you're a citizen of the UK and you live in your house in Bognor Regis in the South of England, and you pay your taxes to the government, and then one day almost everyone around you in Bognor Regis want to break free from the UK. Just because they outnumber you doesn't mean you lose your rights, and the central government is to uphold the law and protect your rights.