What happens if China and Russia form a NATO-esq agreement while Russia takes old USSR countries and China takes Taiwan?
China may be able to take Taiwan. First they have to get enough stuff across the straight. That's not easy. To do it, they have to own the sea and the air, which means that they have to have disabled most of the American assets within hundreds of miles. That's not easy either.
They can form the agreement (the Moscow-Beijing Axis) if they want. "Taking" is harder.
Given that several of those are NATO countries, WWIII if they even try.