The primary cause of the Opium Wars, which began in the mid-19th century between Britain and China, was the British trade of opium in China. The British East India Company grew opium in India and exported it to China, leading to widespread addiction and societal issues. To combat this crisis, the Qing Dynasty imposed strict bans on opium trade, resulting in increased tensions. Britain, driven by economic interests and trade imbalances, responded militarily. The First Opium War (1839-1842) ultimately ended with the Treaty of Nanking, which ceded Hong Kong to Britain and opened several ports to British trade, significantly altering China's sovereignty.