England invaded Ireland during the mid-1840s, displacing the Irish population.
They fled a famine caused by severe overpopulation and a devastating blight on the potato crop.
The expansion of the industrial revolution displaced Irish workers.
Anti-Catholic violence forced the Irish to flee their homeland.
None of those is correct. #2 is half right, in that they did flee a famine, and a blight did devastate the potato crop. But during this period, Ireland produced more than enough other food to feed its entire population. The famine was caused not by the potato blight, but by the fact that the food that was produced was shipped to England.