You could call St. Patrick´s Day one of the original expat holidays. The celebration as we know it today—the greening of the Chicago River and massive worldwide parades—took shape in the U.S. on March 17, 1762 when an Irish faction of the English military, bolstered by traditional music, marched on New York City in a show of national pride. Nowadays, the holiday has taken hold in such far-flung places as Argentina, where the world´s fifth largest Irish population resides.