Final answer:
The longest running military occupation of the 20th century often noted is the US occupation of Japan from 1945 to 1952, during which General MacArthur spearheaded significant democratic reforms and Japan's transition to a peaceful democratically.
Step-by-step explanation:
The longest running military occupation of the 20th century can be debated, but a significant example is the US occupation of Japan, which lasted from 1945 until 1952. During this period, General MacArthur led the American military in overseeing the transition to a democratic government, the drafting of a new Japanese constitution, and enacting broad societal changes. Conditions for Japan's post-war recovery included demilitarization, democratization, and the instilling of respect for human rights. The occupation led to the implementation of a constitution that brought about major reforms and established Japan as a peaceful, democratic country closely allied with the United States.