The US's military expansion (and by extension its defense budget) is directly correlated to its domestic industrial expansion and its need to keep supply lines

The US's military expansion (and by extension its defense budget) is directly correlated to its domestic industrial expansion and its need to keep supply lines flowing. They basically spend a lot because they need to jump over two oceans to afford the economic model they chose. That wasn't the case when the US was still content with self-isolation, before the Spanish–American War.