Why did Japan invade China in 1931, and escalate its efforts in 1937? How did this affect the relationship between Japan and the West?
Before 1852, Japan was mostly an isolationist country with limited trade and contact with the West, and western influences were also strongly discouraged in the country. But due to the convention of Kanagawa, the treaty that opened Japanese ports to US trade changed the scenario, as the terms of the trade were mostly dictated by Americans as they have far superior technology than Japan then. This end of isolation, gave the Japanese a view that they were not strong enough, and they might face the face of Chinese suffering. To escape this fate, the 1868 reform movement started in Japan, which put the country on the path of industrialization. To catch up with the west and not get stomped by them like China, they ended up doing a lot of imitation of west, like the western dressing style, military recreation on the Clausewitzian lines, even their parliament became a rip off of the Prussian parliament. So to fully imitate 19th century European powers, Japan had to engage in imperialism and colonialism to avoid looking weak. So, Korea then looked like a liability to Japan, as it did not reform as Japan did and could have been easily conquered by a western power which could have led to an invasion of Japan. Also, the abundance of iron and coal in Korea made it a good choice for Japan’s colony. But the issue here was that Korea then was a Chinese tributary state where the Korean king paid his tributes to the Chinese emperor. So, Japan could only force Korea to sign unequal treaties, but the Chinese troops sent to Korea in 1894 intended to put down rebellion were not notified to Japan beforehand. This led to the fight which eventually led to the First Sino-Japanese War, which China lost badly, and Korea became a Japanese tributary state. Also, Japan got the island of Taiwan as their colony, and trading and repatriation rights to many Chinese cities.
The second Sino-Japanese war starting in 1937 began with the infamous Marco Polo bridge incident where the dispute between Japanese and Chinese troops escalated into a battle, which eventually ended up with Japan’s unconditional surrender to the United Nations allies of the World War II.
Due to this, Japan’s relations with the west also deteriorated. China fought in this war with aid from Soviet Union and US. And Japan’s Pear Harbour attack on US in 1941, merged the war with other conflicts o the Word war II. Following the Pearl Harbour Attack on US, the US declared a war against Japan, which was joined by China in formal declaration of war against Japan, Germany and Italy. So, all the Western allies entered a war against Japan following the Second Sino-Japanese war.