They always use proxy (Venezuela, iran, Greenland,, etc) , if don't brave, let them live in peace and quiet.
it would be insane to do this, not that it is not possible but there would be very tragic consequences, these country has matching military powers, especially Russia which has the largest and Effective submarines while US leads the air space with their B2 spirit bomber, China and Russia trailing behind, it would really be economic and strategy wise to go for a direct confrontation with these powerful countries.
The best they can do is what they are doing now which is to trying weaken their economic strength and reduce their global influence. More like an indirect war using weaker countries like Venezuela and Ukraine as battle fronts.