Answer:
D. They were protected by the U.S. military
Explanation:
Japan was spending very little money on its military because he was an ally of United States of America and Japan was also forbid to have an army so for that reason Japan was protected by the U.S. military. But this protection was very costly for United states of america so they allow Japan to spend more money on its military in order to defend themselves. Japan spend about 48 billion dollars in 2015 on its military which is about 1 % of its GDP.