What was the main cause of the sino-japanese war?
japan wanted to add the island of formosa to its territory.
japan and china competed for influence in korea.
china’s military became a threat to japan.
china closed its ports to japan.

The main cause of the Sino-Japanese War was that Japan and China competed for influence in Korea. The war took place between August 1st 1894 and April 17th 1895. This was the first time in East Asia that there was a shift in power between China and Japan, where China had been the most powerful force and now Japan became that representation.