To reverse the balance of trade with china, british merchants sold to chinese smugglers.

Opium.

Explanation:

The Opium War (1839-1842) was a military conflict fought between Qing China and the United Kingdom. Great Britain was a major buyer of Chinese luxury goods, such as silk and tea, while British exports to China were comparatively minor. This created a major trade deficit for the British, who also had to pay for the Chinese goods with silver. In order to counter the trade imbalance, the British smuggled opium from India into China. When the Chinese government acted against the opium trade, Britain responded with force. British victory on the war forced the Chinese to sign the Treaty of Nanking, which opened its ports to British trade and ceded Hong Kong to the British crown.

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because of the war the westeners befriended japan and each other advance.