Every year on July 12, many Northern Irish Unionists celebrate Protestant victory in the Battle of Boyne in 1690 by lighting huge bonfires and marching through the streets playing music and saluting the Queen. This year, about 50,000 people reportedly took part all over the region.

"The Twelfth" is a particularly contentious period in the heavily divided Protestant/Catholic city of Belfast. After decades of conflict in Northern Ireland known as the Troubles — a political and sectarian war that claimed more than 3,600 lives — there are still many people on each side who feel oppressed by the other. Riots involving rock throwing, Molotov cocktails, and even gunfire often erupt on or around the Twelfth. Problems are particularly commonplace as marchers head through Ardoyne, a heavily Catholic and nationalist area surrounded by Protestant neighborhoods.

Though the city's youngest adults can barely remember the Troubles themselves, they're increasingly becoming radicalized. Poverty in Belfast is at a 10-year high; unemployment hovers near 8 percent, with about one in four 18- to 24-year-olds out of work in 2013. And so with few jobs and often inadequate education, young men are indoctrinated by paramilitary groups still left over from the fighting of the past.