The U.S/Japan/Military

The United States had proposed in an earlier round that Japan pay 75 percent of the estimated US$10 billion (?8.1 billion) cost of moving the Marines from Okinawa to Guam, a U.S. territory about halfway between Japan and Hawaii.

Japan had said it would pay about a third of that amount, but last week reportedly proposed paying US$3 billion (?2.4 billion) of the cost plus another US$3 billion in loans.

Under a mutual security pact, the United States has about 50,000 troops stationed in Japan. The presence includes more than 10,000 Marines, several air bases and the home port for the Seventh Fleet.

以前も掲載したけど、なんで出ていってもらうのにそんなに金だっせってわけ？それだけ出すなら日本としては核作って自衛力高めたら方がよっぽどコストが少なくすむんじゃないの？
ここらへんの事情に詳しい方教えてください。