Why did the United States and other countries enforce a ban on the export of iron, steel, and fuel to Japan in the 1930s?

They did it because Japan was becoming imperialistic in the South East Asian region and in East Asia, spreading into China and fighting with Russians as well. The US was threatened because they could lose their SEA colonies so they imposed sanctions when Japan left the league of nations and started expanding. This meant that their trading treaties with the US were broken and this made Japan angry.