Fianna Fáil had a tangled birth in the Civil War and first took power in 1932
Sinn Féin split into pro-and Anti-Treaty factions, with de Valera leading the Anti-Treaty faction. Anti-treaty Sinn Féin boycotted the Dáil for several years after the end of the Civil War until a faction around Éamon de Valera split and created Fianna Fáil. They first came to power in 1932 and were long the most popular party in Ireland.
The 1948 election was controversial as Éamon de Valera introduced the Electoral Amendment Act, which was seen as an attempt to ensure the continued dominance of Fianna Fáil. But de Valera failed to retain power after the other parties joined together to create the first coalition government.