Why did Eamon de Valera oppose the Anglo-Irish Treaty?

Éamon de Valera opposed the Anglo-Irish Treaty primarily because it required an oath of allegiance to the British crown, which many republicans found repugnant.12

Additionally, the treaty established the Irish Free State as a dominion with constitutional status similar to Canada, rather than the fully independent republic that de Valera and other separatists had sought. The agreement also allowed for the partition of the island, as it provided Northern Ireland the option to remain part of the United Kingdom.12

Following the Dáil's narrow ratification of the treaty in 1922, de Valera resigned as president in protest, a move that provided significant legitimacy to the anti-treaty faction and contributed to the subsequent Irish Civil War.12