Complex sentence: The Qing administration initially tolerated opium importation because it created an indirect tax on Chinese subjects: increasing the silver supply of the foreign merchants through the sale of opium encouraged Europeans to spend more money on Chinese goods.
Split into simpler sentences: The Qing administration initially tolerated opium importation because it created an indirect tax on Chinese subjects. Increasing the silver supply of the foreign merchants through the sale of opium encouraged Europeans to spend more money on Chinese goods.