Ireland within the British Empire went through a traumatic experience of consolidation of Protestant and English rule, followed by a long gruelling campaign by disenfranchised Catholics to return their rights and later to attempt full independence.

Since the Cromwellian and Williamite conquests, Ireland had been reconfigured to serve the needs of England in both terms of food, labour, and later soldiers for the British army. In 1683, 38% of Irish exports were to England, by 1774 it was 74% and even higher in the 1840s. Through various ‘Penal Laws’ Catholics had been excluded from much of the function of the state, which was controlled by the Protestant Ascendancy, a group of mostly Protestant landlords who acquired their land through the earlier conquests and mainly lived in England.

The 1798 Rebellion inspired by the French revolution was the catalyst in which the London government sought to bring Ireland under direct control. Up to this point Ireland was governed by its own parliament under the leadership of a Lord Deputy appointed by the king, however real control mostly rested in London. A brief moment of legislative independence for the parliament prior to this rebellion led London to believe the Irish parliament could not manage the country and required direct rule.

Although much of the earlier Penal Laws were repealed in the late 18th CE, it was hoped by Catholics that the 1800 Act of Union would rapidly bring about Catholic Emancipation, but this was not to be the case and Ireland would continue to be administered as a colony rather than as an equal partner of a United Kingdom. The Duke of Wellington would even remark “I lay it down as decided that Ireland in view of military operations, must be considered as an enemy’s country.”

Failing to enact Catholic Emancipation led Daniel O’Connell, a political leader, to mobilise the country’s majority Catholic population into a movement that eventually brought about Emancipation in 1829. This went on to inspire the Tithe War against the tithe payment, a tax which was paid towards the Church of England. Although this wasn’t led by O’Connell, the movement managed a level of protests and non-payment that led to their abolishment in 1838. O’Connell was to follow his success of Catholic Emancipation with an attempt to repeal the Act of Union, but this would become overshadowed by the Great Famine in 1845.

The proliferation of the potato had allowed the population of Ireland to grow to 8.175 million by 1841, the majority of those solely dependent on the crop were the labourers of the farms owned by the landlords of the Protestant Ascendancy. When the crop failed in 1845 and again in 1846, the British government attempted to provide relief and did indeed avoid excess deaths, however a change in government in June 1846 saw the introduction of a hard-line laissez-faire policy towards the famine, and an attitude of prejudice, ignorance, and opportunism. The Famine would see up to one million dead and two and half million leave the country.

The experience and loss of the Famine would see the rise of new movements. The farmers that remained would form the Land League to return land to their ownership and would see their success with the introduction of the 1881 Land Act.

Irish politicians in London would take inspiration from O’Connell to repeal the Act of Union and install “Home Rule”. Their efforts would reach as far as the 1914 Home Rule act before being delayed by World War 1, and ultimately diminish as the harsh response by the British army to the 1916 Rising led public opinion to sway in favour of full independence.

Those who emigrated would form the Fenian movement, a precursor to Irish Republican Brotherhood and later the Irish Republican Army that would fight the Irish War of Independence between 1919 and 1922 and ultimately achieve a form of full independence.

I’ll leave the answer here to refer my previous answer on the relationship between Ireland and the UK after 1922.

Sources:

Various, Atlas of the Irish Revolution, Cork University Press, 2017

Various, Atlas of the Great Irish Famine, Cork University Press, 2012

S. J. Connolly, Companion to Irish History, Oxford University Press, 2011

Prior to the 1801 Acts of Union, Ireland was technically a separate Kingdom from England (and after the 1707 Acts of Union, Great Britain) held in a Personal Union by the British Monarch since 1541, but with its own Parliament and essentially entirely run by English (then British) officials.

In the 1801 Acts of Union, passed simultaneously by British and Irish Parliaments, Ireland became a fully integrated part of Great Britain, which is what caused the name change to the United Kingdom of Great Britain and Ireland, because rather than being two Kingdoms with the same King they had now been legally merged into one single title and nation, a United Kingdom. They were given 100 seats at Parliament in Westminster and 28 peerages were entered into the House of Lords.

Following the successful Irish War of Independence (1919-1921), the British Government realised holding Ireland in the current state was untenable, so in late 1921 they threw them a bone, called a ceasefire, and offered them a treaty: become a Dominion in the British Empire, and enjoy all the autonomy that comes with that, and in return simmer down. This would have given them equal status as Australia, New Zealand, Canada, and South Africa, and given them their own Parliament, Prime Minister, and control over domestic policy, but foreign policy was still in the hands of Westminster.

This caused a split in the IRA, some of whom thought this was a great first step towards independence, and others who rejected the idea of continued British rule and wanted full independence right this second. The real kicker though was that under the treaty, members of the Irish Parliament which would be established would have to swear fealty to the King, and the leaders split over the same lines, some agreeing to suffer this and some refusing. They became known as Pro- Treaty or Anti- Treaty respectively. This started the Irish Civil War.

Interestingly, the Dominion status choice was given on a regional basis rather than national, and only 26 of Irelands 32 counties opted in, which is what led to the area we now call Northern Ireland staying a fully integrated part of the UK.

Despite the Civil War which would start in June of 1922, the Irish Free State would come into being on the 6th of December, 1922. The Irish Free State was now a British Dominion. The Civil War in the Irish Free State was short, lasting less than a year (28 June 1922 – 24 May 1923).

From then on there was lots of internal politicking within Ireland about who took their seats and who refused, Eamon de Valera started Fianna Fáil which took over government in 1932, abolished the oath, started an economic war with the UK, and drafted a new Constitution which, if put into effect, would make Ireland a full independent nation.

The Constitution was put to a referendum and passed, it was passed into law on the 29th of December 1937, which changed the country’s name to “Ireland” (not the Republic of Ireland, as it is commonly referred), and full independence declared, and that severed the last legal ties to the UK.

The history of English intervention in Ireland dates all the way back to the 12th century and it is from this period that Ireland’s ‘status’ within the British Empire was set. Of course the British Empire did not yet exist, at least in how people usually think of it (there was the so-called Angevin Empire). So Ireland can therefore be considered Britain’s “first colony” or a “laboratory for empire”. I did write another answer a few months back dealing with the question of whether England “colonised” Ireland or not.

The last few decades of the 12th century saw the rapid military conquest of a politically fragmented Gaelic polity by subjects of the king of England (powerful lords like Richard de Clare, known as Strongbow). Although incomplete, the end result of these initial incursions was a polity known as the ‘lordship of Ireland’. From the time of King John (1199 - 1216) the term dominus Hibernie (‘lord of Ireland’), began to appear as part of the title of English Kings.

Having thus been haphazardly annexed to Henry II’s ‘empire’ in 1171, Ireland remained a divided land, its constituent kingdoms placed under the nominal authority of the Plantagenet kings, with only Connacht recognised after 1175 as a semi independent entity ruled by native kings owing fealty (and a rent, at first of hides, hawks and hounds, only later of sterling) to Henry II and his successors.

Over the ensuing centuries the ‘lordship of Ireland’ would become inextricably bound with the Crown of England, even if the island itself remained politically fractured between areas of direct English control and Gaelic territories which were de facto independent. By 1388 Ireland was being referred to as a 'parcel' of the English crown. The term used for the place in all official records during the middle ages, was terra Hibernie, the land of Ireland. Ireland was a land, just like Aquitaine or any other land under the dominion of the king of England.

Because he exercised dominium over this land, the king was thus dominus Hibernie as noted. It was not a separate legal entity, but something vested in the English crown. This relationship was the basis of Ireland’s relationship to England. Alhough there are various complexities that derive from this I don’t think here is the place to go into it. There were all kinds of moral, political and historical claims to justify the English Crown’s claim to Ireland. Along with the the alleged papal bull Laudabiliter and the idea that the English would bring a kind of ‘civilising mission’ to Ireland, Gerald of Wales (Gerald de Barri) would also write in the 1180s of England’s ‘fivefold right’ to Ireland. This included far more elaborate pseudo-historical claims derived from the ancient past. Claims which would continue to be rehearsed like clockwork into the early modern period.

In any case, James Lydon has suggested that by the mid-thirteenth century:

‘the doctrine of inalienability had been clearly defined. The lordship of Ireland could no longer be separated from the English crown’.

A resurgence in native Irish power and the “Gaelicisation” of a number of the descendants of the earlier English colonists meant that the actual limits of this authority were often considerably less than in theoretical terms. But as far as the status of Ireland within the British state, Ireland was in theory an appendage to the English crown.

This medieval lordship would be transformed into a separate kingdom with the Crown of Ireland Act 1542 (enacted in 1541), with which the Irish parliament - an English parliament in Ireland might be a better way to put it for those unfamiliar - proclaimed Henry VIII the first English king of Ireland.

Previously, an Irish parliament in 1536 had enacted a statute that 'the land of Ireland is parcell of the crown of England, governed by one prince and lord'. Then, with the passing of the new act of 1541 they:

"enacted, ordained and established by authority of the present parliament that the king's highness, his heirs and successors, kings of England, be always kings of this land of Ireland'.

Their kingship was to be forever 'as united and knit to the imperial crown of the realm of England'. Of course, there are complexities here too that you can read more about in the answer linked above. Ireland was a ‘kingdom’, but in practical terms the reality could be much different than this might imply.

The kingdom of Ireland later passed, along with England and Wales, from the Tudor dynasty to King James VI of Scotland (then James I of England and Ireland). At this stage (Ireland became one part of a multiple or composite monarchy under the Stuart dynasty in the early and mid-seventeenth century. The ‘Three Kingdoms’ of England, Scotland and Ireland were united kingdoms only through the personal union of the monarch. They retained separate parliaments and legal structures even if each was part of the wider Stuart domain (Wales had already been annexed into the Kingdom of England in the 1530s).

The United Kingdom as an actual political entity was created in 1707 with the union between Scotland and England. Later still Ireland itself would be incorporated directly into the United Kingdom in 1800. Thereby becoming another constituent part of the new state, though I note that some other answers have already provided some information on the post 1801 events.