Most immigrants came from Ireland due to the potato famine.
Explanation:
One of the most devastating things to happen to Ireland was the potato famine where millions of people died of starvation in a famine tat was largely avoidable but the British did not do anything about it.
A huge stretch of the population thus decided to move away from the nation to settle for better prospects and the majority chose US.
The US thus became swarmed with migrants from Ireland on its shore that wanted sanctuary.
Most liked the idea of joining the USA and of course did not resist. It is said that they accepted it with a fatality like which they accepted small pox,tuberculosis and hook worms. the worst that happened was dogs barking at US soldiers passing through.
