Along with the Soviet Union, consider the Ottoman Empire -- its great days were past, but it tottered on into the 20th century. A series of mis-steps and poor rule sealed their fate. The empire broke into pieces and the Arabs inherited a series of bastard kingdoms, while the Turks retained only Asia Minor.
At the rate we're going, I think the United States may become something like Greater Texas, while the Liberals will inherit bastard kingdoms on the coasts and along the Great Lakes.