Complex sentence: The Soviet Navy was formed in 1917 from the remnants of the Imperial Russian Navy, which had been almost completely destroyed during the Revolution of 1917, the Russian civil war, and the Kronstadt rebellion.
Split into simpler sentences: The Soviet Navy was formed in 1917 out of the remnants of the Imperial Russian Navy. The old Russian Navy was almost completely destroyed during the Revolution of 1917, the Russian civil war and the Kronstadt rebellion.