The US has the highest GDP in the world (unless you count that mess called the EU a country). Since we have such a huge economy and society we spend a lot over all, so by extension all our government expenditures will be higher.
Now in terms of military expenditures as a % of GDP we are high but not even in the top ten. We rate #11 globally with 11 other countries within 1% below us.
China go pester Eritrea about their defense budget, they are spending over 20& of their income on it!
They must be up to something! 