What is a long-term consequence of the historical development discussed in this 1839 letter?

The consequence of the historical development in long term that is being discussed in this 1839 letter is : setting up of British sphere of influence that is done  in China.

Therefore this agreement results setting up of the British sphere of influence that is done in China.

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Establishment of the British sphere of influence in China

Explanation:

Following the letter written by Chinese Commissioner Lin Zexu to Queen Victoria of Great British in 1839 concerning the trade of opium. The aftermath event led to a war that was referred to as the Opium War between Great Britain and China.

With the British winning the war, the two countries entered an agreement known as the "Treaty of Nanking" in 1845. The treaty which sometimes called "Unequal Treaties" is finally led to the "Establishment of the British sphere of influence in China."

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