Why is St. Patrick's Day such a big holiday in the US?

If you go for an afternoon stroll around the streets of Chicago, Boston, or New York City on the weekend of St. Patrick’s Day,

you should be prepared for crowds of revelers, likely wearing green with a Guinness in hand.

 This party atmosphere belies the political nature of both the holiday and the mass immigration of Irish people to the US.

The annual celebration of St. Patrick’s Day has become tradition across the US,

mainly due to the massive number of Americans with Irish roots.

More than 1 in 10 people in the US have ancestors who left Ireland, including US president Joe Biden, who proudly proclaims his ties to Ireland.

The vast majority of Irish immigrants to the US left during the great potato famine,

 fleeing a period of starvation and disease that lasted from 1845 to 1852 and killed more than 1.9 million people.

 During the same span of time, roughly a quarter of the country left in what is considered one of the largest exoduses in history.

The famine was due to potato blight—a fungus that caused the degeneration of potato crops across the country,

which was essentially the only crop Irish farmers could grow.