he was arrested and jailed by the British authorities, first being sent to Belfast before being transferred to Wormwood Scrubs, London. He was released in April 1920 following his participation in a mass hunger strike by Irish prisoners against their imprisonment. Following his release, he became Officer Commanding of the West Donegal Brigade of the Irish Republican Army and fought in the Irish War of Independence. During that time he rose through the ranks and became the commanding officer of the 1st Northern Division. Following the end of the War of Independence and the signing of the Anglo-Irish Treaty, Sweeney chose the Pro-Treaty side in the Irish Civil War. In the lead-up to the civil war, he was involved in smuggling arms across the border to northern nationalists, which lead to clashes with British troops. During one such clash seven of his men were killed at Pettigo. In 1921 he was one of six Sinn Féin candidates elected unopposed to the House of Commons of Southern Ireland for Donegal. Again he did not attend and instead participated in the Second Dáil. In 1922 he was re-elected as a Pro-Treaty Sinn Féin candidate for Donegal and participated in the Third Dáil. During the Civil War, he was made a General in the newly formed National Army and placed in command of its units in the North-West of the Island. The period saw Sweeney execute a number of captured Republicans, including a former friend, Charlie Daly. Life in the Irish Free State In 1923 he choose to leave politics and did not try to retain his seat as a TD. Instead, he remained in the National Army. In 1924 he was briefly acting Chief of Staff during the Irish Army Mutiny. By 1929 he had risen to the rank of Chief of Staff proper, a promotion that happened to coincide with the rise of Fianna Fáil to government. Many feared an outbreak of violence once again if Cumann na nGaedheal did not accept this change. Sweeney declared his view on the matter, stating that the will of the people would be protected under his command. Sweeney remained in the Army until his retirement in December 1940. He later became Secretary of the Irish Red Cross in the Republic of Ireland. Having spent most of his life in Dublin, he died in 1980 aged 83 before being buried in a full military ceremony