When and why did the irish start immigration to america in large numbers

When the famine began in 1845, many people began to emigrate from Ireland, many of those going to America. There would have been some emigration to America before that, but the famine increased the numbers going.

Explanation:

lincoln presided over the union victory in the american civil war, which dominated his presidency. a former whig, lincoln ran on a political platform opposed to the expansion of slavery in the territories. his election served as the immediate impetus for the outbreak of the american civil war.