Modern conditions do not allow to isolate their country from the rest of the world. Who said that the Americans are funding an army of Europe and Japan? Another thing is that Americans have to help their allies, while pursuing America's interests.
The United States is maintaining large military bases in Europe and Japan, and the funds for maintaining them comes from the American treasury. This needs to change. The EU/Japan also needs to share the expenses.
Do not forget that American military bases. The country that offers land for construction of military bases should not have to bear the financial burden of maintaining them. These bases guard the interests of America.