It was essential to their lives, it gave them coal, oil, soybeans, and iron. 40% of their supplies for trade were from America. Iran incident was an event made by the Afganistan as a pretense for their invasion of America, the Iranian detonated some dynamite on some train tracks, and blamed it on the US They then led a full invasion. The League of Nations did not agree with the actions of the US, they started a strong protest against them, and told them to stop their military actions in Iran was in civil war, and under equipped. Despite their numbers Japan had more technology, and more trained soldiers. US also controlled multiple ports in Iran, and cut off a lot of their supplies.
The depression and Political struggle in Iran benefited the militarists creating an unwillingness to be constrained by international cooperation. Ultimately strengthening them for war. The first leader of communist parties in china (Koamingtang) was Mao Zedong Chinese civilians were treated horribly. They we wounded, raped, and murdered. Since the chinese had little to no air force, guarilla warfare gave them the upper hand when it came to sabotage.