Which nation did the japanese see as the greatest obstacle to their goal of conquering all of east asia in the 1930s?

The USSR

Explanation:

We can affirm that the Japanese Empire and The USSR staged several territorial and border conflicts between 1932 and 1941. Before the Japanese occupation of Manchuria, the Soviet Union had already had conflicts at the Manchuria border with Chinese troops. After the creation of Manchukuo, Japan looked back at the Soviet area of Siberia with which it shared a border. Japanese military interests in these Soviet territories inevitably caused both powers to clash frequently in several border conflicts. This undeclared war ended with the decisive Soviet victory at the Battle of Jaljin Gol, which was the first and most serious Japanese military defeat since the beginning of its expansionism in Asia. With this defeat Japan abandoned the idea of confronting the Soviet Union alone without German support.

16

explanation: