"Anti-Treaty" refers to the faction in Ireland that opposed the Anglo-Irish Treaty signed in 1921. This treaty established the Irish Free State and granted limited self-governance while still recognizing the British monarch. The Anti-Treaty side believed the agreement compromised Ireland's full independence and sovereignty. The opposition led to the Irish Civil War from 1922 to 1923, where Anti-Treaty forces fought against the pro-Treaty government. Key figures in the Anti-Treaty movement included Éamon de Valera and Michael Collins, who had differing views on the treaty's implications for Ireland's future.