EVERY March, for about a week, Dublin’s corridors of power empty out. Government ministers and officials pack their bags as part of an annual soft-power push like no other. They head abroad on promotional trips linked to St Patrick’s Day, the Irish national holiday that falls on March 17th. This year, 35 countries will play host to high-ranking Irish officials, but many more will stage their own celebrations of Irishness. The highlight of this diplomatic assault is the annual meeting between the Irish taoiseach, as the prime minister is known, and the president of the United States. Few countries enjoy such high-level access and exposure on their national day. But how did the celebration of a devout fifth-century missionary become a global phenomenon when people drink whisky, dress up in green and demand that people kiss them because they are Irish, even if they are not?

Emigration has been at the heart of it. During and after the famines that afflicted Ireland in the 19th century, some 2m people left the island, the majority settling in America and Britain. By the 1850s, the Irish accounted for up to a quarter of the population of cities like Liverpool and Boston. Within these communities, an Irish identity emerged based on a strong Catholic faith and the political cause of the day: independence from Britain. This nationalist identity was especially celebrated on St Patrick’s Day when, in America and elsewhere, public sermons and orations celebrating Irish heritage became common. In 1852, the Catholic archbishop of New York noted that not only do the Irish “cherish fond memory for the apostle of their native land, but they propagate it, and make the infection as if it were contagious”. 

Soon the contagion caught on. By the mid-20th century the holiday had evolved into a celebration of all things Irish, and was well established across America. With some 40m Americans claiming Irish heritage it also presented an opportunity for American politicians to curry favour among the diaspora. Irish migrants had long been victims of prejudice, but that changed as the 20th century wore on. The wariness shown in job advertisements declaring “Irish need not apply” gave way to a more positive image of witty types, who were not averse to an occasional glass of the strong stuff. This helped to fuel the idea of St Patrick’s Day as an excuse for a party. That the Irish had managed to work their way up the social ladder in the cities where they made their home added to their image as plucky underdogs. 

In Dublin, the national festival can bring in as much as €70m ($87M), according to one estimate. And now there is the Global Greening, in which landmarks from the Great Wall of China to the Eiffel Tower in Paris are bathed in green light. Celebrations have even been held on the International Space Station. Business deals are struck on trade missions and dignitaries take the opportunity to be snapped having the craic with pints of Guinness in their hands. Pubs heave, parades march and for one day revellers raise a glass to Ireland and its patron saint.