Greetings! This question certainly covers a fair bit of breadth and depth in terms of imperial history, and serves a great starting point for discussions on how important "settling" to-be colonies and imperial possessions was for the formation of European empires. I shall be talking mainly about the British Empire in this response, as the French Empire is beyond my area of research and thus my current body of knowledge. Before we begin however, I should note that parts of this response have been adapted from this previous one about settler colonialism in the British Empire, so go give that a read if it sounds interesting as well. With that out of the way, let's begin.

Settling In

"When Englishmen speak or think of the British Empire, they are apt to leave India out of sight, and to think only of the colonies that were founded and largely peopled by the men and women of our own race."

- Viceroy of India Lord Curzon (r. 1899-1905)

Long before Lord Curzon made the comment above, there had been a longstanding process of migration from the Home Isles to the various settler outposts in the "settler colonies" of what would become Canada, New Zealand, Australia, South Africa, and the United States of America. The first destination however, for English families, was neither of these massive tracts of land. In fact, the first destination which the government in London actively encouraged their citizens to move to was Ireland. From the 1550s onwards, English settlers often moved into Ireland at the urging of the government to take control of land and estates confiscated from various Irish lords and clans who had "rebelled" against the rule of England. At the turn of the 17th century, there were perhaps 4,000 such settlers in Munster and Leinster (near Dublin) respectively. During the 1600s however, this number shot up. By the 1640s, more than 100,000 people from the mainland had settled in Ireland, far more than had dared to cross the Atlantic at the time. After the Battle of Boyne in 1690, part of the Williamite War in Ireland, which saw the Jacobites under the deposed King James II lose decisively to those of King William III, 80,000 more settlers moved into Ireland rapidly.

Whilst the Williamite War (also known as the Jacobite War in Ireland) was raging, the number of Atlantic migrants had also risen. Nearly 400,000 people had crossed the Atlantic to the Americas by 1700. For majority of them, the destination was not the mainland "13 Colonies", but rather the plantations of the Caribbean. The toll of mortality at the time meant that only an estimated 230,000 managed to survive the journey (50,000 of whom also weathered the tropical climate of the Caribbean). In total, during the seventeenth century alone, it is estimated that around 1 million people (70% of them English) left the British Isles.

Why exactly did they leave? The answer might perhaps be found in several key factors. The first has been touched on already: the extreme instability which affected much of the British Isles for the seventeenth century. Constant civil strife, rebellion, repression, and civil war meant that migration was a means of escaping the carnage and seeking sanctuary beyond the shores of the Home Isles. Yet for a grand majority of the settlers, there was another motivator: economic opportunity. The poor harvests and economic depression back home propelled many single men (and in some cases, entire families or communities) to seek greater profit elsewhere. This was particularly the case with the plantations of the Caribbean, where many Englishmen came to seek a quick fortune working in the sugar, tobacco, or gold trades. Subsequently, this idea of a link between conditions in Britain and migration is strengthened by the fact that fewer settlers departed from 1700-1760, when the influx of African slave labour to the Americas and the stabilisation of affairs back home meant that the "white settler" had little need to seek economic security beyond the British Isles. We can see this pattern emerging again after 1760, when economic downturns back down and the publicity brought to America as a result of the Seven Years War prompted a new wave of migrants. Between 1760 and 1775 (when the start of the American revolution put a sudden halt on immigrant traffic), an estimated 125,000 people from the British Isles (mostly Scots and Protestant Irish) crossed the Atlantic.

Yet the economic conditions alone cannot fully explain the motive to migrate. Ideology also played a role here, in two distinct shapes. The first of these was the "elitist" ideology of free trade, which rose in popularity amongst the economists and manufacturers of 19th century Britain. Under this idea of "progress", the goal of economic improvement was second to none, and any social costs was seen as a necessary evil in pursuit of that goal. It was a fairly commonly-held belief among English economists of the day that the only way to solve Ireland's poverty at the time was by mass-migration, though preferably not to England. Alongside this ideology of the landed elite and the gentry, there was the popular ideology of property rights and a sort of "economic respect" which John Darwin outlines further:

"Notions of a 'just' wage, and of the respect owed to skilled work fuelled bitter resentment against 'industrial' employment and 'factory discipline'. More rooted still was the idealization of property, of the right to cultivate a plot of land if not as a main income then as an insurance against old age and misfortune...If migrants were pushed out by economic hardship or worse, they were also pulled out by the lure of free or cheap land, the huge social magnet that was dangled before them by rival destinations in America and Australasia."

This was developed further by the contemporary radical free trader Richard Cobden, who believed that settler-commerce would bring with it great influence from the Home Isles to the native populaces of a region, declaring in 1836 that:

"Not a bale of merchandise leaves our shores, but it bears the seeds of intelligence and fruitful thought to the members of some less enlightened community...[O]ur steamboats and our miraculous railways are the advertisements and vouchers of our enlightened institutions."

As such, it was this economic-ideological mix which often dictated how heavily (or indeed, how lightly) a territory would be inhabited by European settlers. Australia for example, despite its harsh environment and vast distance from Britain, was declared terra nullius (nobody's land) by the British who first landed on its shores. As a result, the rights of the Aboriginal populations to the land were often ignored by the settlers, and the British government continually faced legal problems when dealing with "native" resistance. The sheep farmers, convicts, and settlers of Australia had an entire landmass worth of land to (attempt to) profit from, and attempt it they did. John Darwin on this drive to push the settling of to-be colonies further:

"Claiming the land, exploiting the soil, remaking the landscape, putting down roots, excluding all rivals were all stressful endeavours: scruples were costly and doubts might be fatal. The hard racist edge of settler society was the product of fear and anxiety as well as of arrogance. It reflected the pressure, all but relentless, to move restlessly forward in case stagnation set in and the experiment failed.'Populate or perish' became a political cry in one settler society. As a populist motto, it fitted them all."

Thus then, this economic consideration was key in the trends of migration and settlement in various parts of the empire, but do not be swayed into thinking that it took precedence over every other consideration out there. Whilst the "lure" of economic opportunity often formed the motivation for settlement en masse in the expansion of the British Empire, it cannot serve as the sole reason in areas where settlement was not quite as rapid or indeed, successful.

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