Complex sentence: By the end of the war in 1945 by liberation in Hong Kong by joint British and Chinese troops against the Japanese during the Second Battle of Hong Kong, the population of Hong Kong shrunk to 600,000, less than half of the pre-war population of 1.6 million.
Split into simpler sentences: By the end of the war in 1945, Hong Kong was liberated by joint British and Chinese troops in the Second Battle of Hong Kong. The population of Hong Kong had shrunk to 600,000; less than half of the pre-war population of 1.6 million.