Final answer:
Manchuria was renamed Manchukuo by Japan in 1932 after it was invaded by the Japanese Imperial Army in 1931 and set up as a puppet state with the former Chinese Emperor as its nominal head.
Step-by-step explanation:
Japan changed the name of Manchuria to Manchukuo in 1932, as part of its aim to establish itself as a preeminent power in Asia. This occurred following the invasion of Manchuria by the Imperial Japanese Army in 1931, leading to the setting up of Manchukuo as a puppet state the following year. The Japanese Kwantung Army convinced the former Chinese Emperor Pu Yi to head the government of Manchukuo, and by March 1932, he had been instated as 'chief executive'. The formation of this puppet state was part of a broader Japanese strategy to create an economic and military foothold in the region, utilizing Manchukuo's rich coal and iron ore deposits to serve the interests of the Japanese Empire.