Sinn Féin for nine years. (It merged with two other organisations to form Fine Gael in 1933.) Anti-Treaty Sinn Féin members continued to boycott the Dáil. At a special "Ard Fheis" in March 1926, de Valera proposed that elected members be allowed to take their seats in the Dáil if and when the controversial Oath of Allegiance was removed. When his motion was defeated, de Valera resigned from Sinn Féin; on 16 May 1926, he founded his own party, Fianna Fáil, which was dedicated to republicanising the Free State from within its political structures. He took most Sinn Féin TDs with him.
Éamon de Valera the IRA dumped their arms rather than surrender them or continue a now fruitless war, de Valera returned to political methods. In 1924, he was arrested in Newry for "illegally entering Northern Ireland" and held in solitary confinement for a month in Crumlin Road Gaol, Belfast. During this time, de Valera came to believe that abstentionism was not a workable tactic in the long term. He now believed that a better course would be to try to gain power and turn the Free State from a constitutional monarchy into a republic. He tried to convince Sinn Féin to accept this