Famine

Responding to Andra's post:

In your post, you comment that, "However, the potato famine was not created by the British, which means that the Irish left the homeland due to a natural disaster, if I may call it that, rather than because of their oppression by the British." You also inquire as to whether there might be a trend in people emigrating from their homes because of oppressive occupations.

While the actual famine wasn't created by England, the British government caused many of the ensuing repercussions. Namely, under British rule as previously mentioned, Irish Catholics couldn't own land, which meant that they were forced to rent plots of land from British landlords. Because the plots were so small, Irishmen chose to cultivate potato rather than grain, as a plot would yield three times the amount of potatoes as it would grain in a year. Potatoes also were one of those foods that really stuck to the ribs. One acre of land would feed a family for a year. When the blight struck, the Irish found themselves unable to pay their rents or feed their families.

Yet, as the British watched the Irish struggle, their "relief efforts" first took the shape of economic reform. In 1846, the Corn Laws were repealed in a belief that a free market would help alleviate the famine; however, the Irish were too poor to buy the newly available grain.

Relief also came in the form of soup kitchens, but these gradually dwindled as England suffered a banking crises and had to withdraw many of its efforts. Ultimately, "aid" came in the form of workhouses (more on this later). So, while the famine, the blight, the rot was not some sort of biological warfare waged on Ireland, England did little to help, and more to exacerbate the problem.

Source: here