Complex sentence: The power contest between the allied Military Committee and the Regionalists against the National Command were fought out within the party structure; however, the Military Committee and the Regionalists managed to turn the party structure on its head.
Split into simpler sentences: The power contest between the allied Military Committee and the Regionalists against the National Command was fought out within the party structure. However, the Military Committee and the Regionalists managed to turn the party structure on its head.