Which event is most directly related to the 19th century situation described in this passage? (1) signing of the treaty of nanjing (2) russo-japanese war (3) monarchies were restored throughout europe. (4) the slave trade with south america was eliminated?

I believe the answer is: 1.Signing of the Treaty of Nanjing
The signing of The treaty of nanjing Marked the end of the Opium War between the British Empire and the Qing Dinasty.
The treaty heavily favored the British Empire both economically and politically, and made China became a very desirable target for the nations that aimed to expand their territory (such as Japan)