Complex sentence: The abolition of the Parliament effectively ended Southern Ireland which was not a country however, it was not until the establishment of the Irish Free State on 6 December 1922 under the terms of the Anglo-Irish Treaty, that Southern Ireland formally ceased to exist.
Split into simpler sentences: The abolition of the Parliament effectively ended Southern Ireland, which was not a country, however. It was not until the establishment of the Irish Free State on 6 December 1922, under the terms of the Anglo-Irish Treaty, that Southern Ireland formally ceased to exist.