But they don't, so talking about those "what if"s are pointless. China's current interests — and, broadly speaking, those of capitalist Russia even after the USSR has been overthrown — are mostly in line with the Global South's against imperial core countries. There's a reason sentiment like this is common across the developing world.
Many of western countries' victims, like Cuba, DPRK, Burkina Faso, Palestine, etc., would not be able to function right now, or perhaps even exist, if they did not have China and Russia's support. Of course, alot of them like Libya aren't able to function anymore.
Thing is, there is no "trying" to do something on a national scale. What nations do — what they can do — and how they react entirely depends on their mode of production and material conditions. And that mode of production for the US is imperialist capitalism.