Unlike monarchy/communism/fuedalism etc where power and resource allocation are by necessity mostly centralised, capitalism can (and wants to) be divorced from power, and only do resource allocation. Constant realigning it with power (e.g. regulatory capture) is what corrupts it.
The sort of (limited) power capitalism creates is by creating value in some way: labour, capital, contacts, resources. It's not derived from strength, unlike the other methods.
Of course a government, that is fundamentally derived from strength, and must be, can still fight wars. It can do it much better in fact because its economy was organised by the most efficient manner anyone's ever discovered, and so there's a surplus to tax and an efficient economy to flow requirements through.