Curried potato salad - perfect side dish for your barbecue party! | in my Red Kitchen

Curried potato salad

Curried potato salad - perfect side dish for your barbecue party! | in my Red Kitchen

Can somebody please explain why the Americans celebrate Saint Patrick’s Day, which is an Irish holiday?

My sister is visiting and I explained it to her as ‘the Americans just like holidays, so they adapted this Irish holiday’.
But please tell me if I’m correct and besides that… Whát are we actually celebrating? I know about the green color, the clovers and those leprechauns. But why? And how?