Answer:
Japan decided to expand it's empire to obtain resources.
Explanation:
Japan was forced to trade with foreign powers, but didn't have many resources to trade, so Japan was essentially forced to trade things it didn't have. Because of this, Japan was forced to obtain resources. The best way to obtain resources is to invade a neighboring country that does have those resources.
1. The Pax Mongolica (1 century of peace w/ neighboring people under mongol rule)
2. Unifaction of Russia
3. The Pax Mongolica reopened of silk road routes from Asia to Europe
