Complex sentence: Following the Anglo-Irish Treaty of 1921 responsibility for posts and telegraphs transferred to the new Provisional Government and then, upon the formal independence of the Irish Free State in December 1922, to the Free State Government.
Split into simpler sentences: Following the Anglo-Irish Treaty of 1921, responsibility for posts and telegraphs transferred to the new Provisional Government. Upon the formal independence of the Irish Free State in December 1922, and then transferred to the Free State Government.