From my previously gained knowledge from my Japanese classes, the answer would be D. Because Japan didn't really that much of a population boom until the 20th century because they whole island was not yet inhabited. They didn't really feel like spreading Buddhism because it didn't become a popular religion until the 20th century, and the US had nothing to do with Japans wanting of more land. They gained land mainly from China, so the long-standing rivalry between China and Japan would be the best answer.
