I'm not worried about China. The nation follows every international law and doesn't intervene in foreign countries' politics. It strictly adheres to an economic instead of a military agenda, but if the US developed a NATO-like military base in Taiwan, China could potentially react.

The US intends to maintain unipolarity at all costs, and Russia refuses to accept US demands. Tensions will reach a break point, and as the US loses global dominance, I fear it will resort to drastic measures. Russia may lose her temper and do something stupid, but as long as the country isn't cornered, pursuing a stronger global presence doesn't entail blowing up the world.

I think the US would threaten nukes as a last attempt to coerce a nation into submission. Confronting the shifts in global economics and power is difficult on a good day, and the US won't let go easily. Unfortunately, decent, strong leadership vanished from the globe, and we're all led by greedy, immoral egomaniacs, so who knows what's in store for us.