In 1910 the Liberals had been re-elected to Parliament as a minority government. They relied on the support of Labour and Irish Nationalist MPs to remain in power. In 1912 the Liberal government in Britain introduced the Third Home Rule Bill to Parliament.
Although it was successful in the House of Commons the House of Lords blocked it. However in 1911 the Parliament Act had been passed which meant that the Lords could only delay a bill for two years and not stop it completely.
This two years delay was used by the Unionists to prepare for armed resistance to Home Rule should the need arise. In 1912, half a million Protestant men and women signed the Solemn League and Covenant.
In January 1913, the Ulster Volunteer Force was formed and a hundred thousand men signed up.
They set about organising themselves along military lines. In November 1913 the Nationalists followed suit and the Irish Volunteers were formed. Both organisations set about arming themselves.
Text from the Ulster Covenant