You ask why your ancestors might have left Ireland. I am sure they left for the same reasons that 2 million others did. To find work. Ireland has very few natural resources (no oil, coal, iron ore etc) and so did not benefit from the industrial revolution in the 1800s, the way Scotland, England, the US, Canada & Australia did, which created hundreds of thousands of comparatively well-paid new jobs in new industries (coal mining, steel making, ship building etc). So that was a big pull factor. There had also been a huge population explosion in Ireland going up from about 3 million people in 1750 to 8 million in 1830. There simply weren’t the jobs for all those people. In much of Ireland the only employment was subsistence farming, topped up in Ulster with a bit of weaving. And then the straw that broke the camel’s back, along came the famine, numerous times throughout the 1800s. The worst of the famine was not until the late 1840s but there had been several partial potato crop failures before that. People poured out of Ireland all through the 1800s. Two million emigrated and a further million who remained died.