US Invasion of Japan?

Maybe this should be in the Anime section but thought /politics can provide a better answer.

There have been some Anime where the plot consist of the US Army coming into Japan with the intent to try take over Japan under guise of "helping" the country. Anime such as Patlabor 2, Re: Cutie Honey & final eps of Gasaraki.

What started this sort of senario in Japanese politics?

The US is a threat to Japan because of nukes.  A stereotype of US government in anime is "the guys who we respect because they have nukes and we don't want to be obliterated."  Basically they'd rather be allies than enemies, similar to our view of Russia, china, and North Korea- we'd rather not have Nuclear war, but the "what if" scenario is always there in the back of people's minds.  What if some crazy government leader came into office and... oh nevermind. 

Silent Service  shows some political views, although it's not a believable movie.