Complex sentence: The rebellion managed to consolidate support from various groups including the peasants, the Cossacks and Old Believers priesthood and its administration claimed, at one point, control over most of the territory between the Volga River and the Urals.
Split into simpler sentences: The rebellion managed to consolidate support from various groups including the peasants, the Cossacks and Old Believers priesthood. At one point, its administration claimed control over most of the territory between the Volga River and the Urals.