Complex sentence: After the Opium War, the British army pirated many history and geography collections from the Chamber, followed by thefts from local thieves; by 1940, the collection dwindled to less than 20,000 volumes.
Split into simpler sentences: After the Opium War, the British army took many history and geography collections from the library. They were followed by thefts from local thieves; by 1940, the collection dwindled to less than 20,000 volumes.