China spends less than 2% of their GDP on the military (~1.7% his year) and has been since it briefly hit 2% twenty five years ago. If they were in NATO US senators would be calling them deadbeats and Trump would be threatening to kick them out for it.
They're not aggressive. They're a big country, but they're not even really that big in absolute military numbers. They spend about a third what the US does, less than a quarter of NATO, they have about a quarter of the aircraft the US does, most of which are a lot older, about half the naval tonnage and a lot less firepower, about a tenth of the nukes, one overseas base versus over 800 American ones... the only thing that's even comparable is the raw number of army soldiers which is ~60% larger, for a country with more than 4x the population.