The Troubles in Ulster (1920–1922) begin with a week of sectarian violence in Derry.

The Troubles in Ulster of the 1920s was a period of conflict in the Irish province of Ulster, from June 1920 until June 1922, during and after the Irish War of Independence and the partition of Ireland. In Ulster, it was mainly a communal conflict between unionists, who wanted to remain part of the United Kingdom, and nationalists, who backed Irish independence: the unionists were mainly Ulster Protestants and the nationalists were mainly Irish Catholics. During this period, more than 500 people were killed in Belfast alone, 500 interned and 23,000 people were made homeless in the city, while approximately 50,000 people fled the province due to intimidation. Most of the victims were Nationalists (73%) with civilians being far more likely to be killed compared to the military, police or paramilitaries. In Belfast where Catholics made up only a third of the population, the disproportionate number of Catholic casualties combined with sustained attacks upon Catholic civilians involving police or special constabulary forces, led to the troubles being known as the 'Belfast Pogrom(s)'.