Why did japan invade manchuria in 1931? a.) to gain a buffer zone between japan and china b.) to react to chinese aggression c.) to gain access to its natural resources d.) to take back what had previously belonged to japan

The answer is c. to gain access to its natural resources. Japan was building up its industry at the time but lacked the resources to do so. They used the Mukden incident to justify their invasion of Manchuria.  Upon conquering Manchuria they established a puppet state of Manchukuo. This however, resulted to Japan being diplomatically isolated and later withdrew from the League of Nations.