Complex sentence: The Bolsheviks firstly assumed power in Petrograd, expanding their rule outwards, eventually reaching the Easterly Siberian Russian coast 4 years after the war in Vladivostok, an occupation that is believed to have ended all significant military campaigns in the nation.
Split into simpler sentences: The Bolsheviks firstly assumed power in Petrograd, expanding their rule outwards. They eventually reached the Easterly Siberian Russian coast in Vladivostok, 4 years after the war began, an occupation that is believed to have ended all significant military campaigns in the nation.