[yamtaddle]

The US is obviously the global Big Dog, but NATO's got three other top-ten-by-expenditure militaries in it, plus two more of the very-small count of global nuclear powers (Britain, France), and three of maybe a half-dozen countries with notable navies that aren't the US (Britain, France, Italy). Expanding to look at the top-20 by expenditure, you pick up another five entries that are NATO members.

The rest of NATO gives you basically another China's worth of military (they're #2 by spending), so it's not nothing, to put it mildly.

The geography controlled by and the economic power of the bloc is also important, for logistical reasons. Having not just open trade and maybe some donations in wartime but outright military support for your supply lines is huge, plus intel sharing and such.