system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is the military spending of the US ($682 billion) justified when it's 4 times more than that of the 2nd highest? ($166 billion - China). Are we really being threatened that much?
gpt
In terms of coverage and force projection the US is unmatched.  They feel the need to have these capabilities in order to protect american interests in foreign lands.  Meaning, it's not the US itself that is under the threat. But rather American businesses, factories, mines, refineries, and ships that are under threat and must be protected.  In addition to this, the US military is expected to protect US soil. 

A country like China on the other hand, is much more concerned with protecting the homeland.  So they keep the military that they do have closer to home, and this is much cheaper.

On an individual technological level the US likely has a slight edge over a country like china.  But it is not a significant contributor to the budget difference.  That is almost all down to the US's want to be able to hit a target anywhere in the world with relatively little notice.  No other country has full world coverage like that, and it costs.