Complex sentence: Zhou's diaries and letters from his time in Tokyo show a deep interest in politics and current events, in particular, the Russian Revolution of 1917 and the Bolsheviks' new policies.
Split into simpler sentences: Zhou's diaries and letters from his time in Tokyo show that Zhou was also deeply interested in politics and current events. In particular, he was fascinated by the Russian Revolution of 1917 and the Bolsheviks' new policies.