By the beginning of the 20th century Catholic Derry was dominated by parliamentary Irish nationalism. Nationalist leaders and the Catholic clergy resisted any republican presence, even opposing the Gaelic Athletic Association as a ‘republican influence’.

Although nine men from Derry were interned after the 1916 Easter Rising, it was not until 1917 that the first Sinn Féin “club” was formed in the city. Sinn Féin won the City of Derry Westminster seat in 1918 after an electoral deal with nationalists. In 1920, this alliance secured a majority in the Corporation election, and nationalist Hugh C O’Doherty became the first Catholic mayor of the city since 1688. The 1922 gerrymander restored unionist minority rule. In response, nationalist councillors boycotted the Corporation for the next ten years.

In the spring and summer of 1920, during the War of Independence, 40 people were killed in the city in clashes between republicans and an alliance of loyalists and British forces.

When the Government of Ireland Act was passed in 1920 Derry remained a part of the north of Ireland, kept by the Unionist government largely because of the unionist symbolism in the city of the Siege and the Walls.