What if the Ming dynasty was able to hold on to power more effectively in the 1620s, on the eve of the Manchu invasions? If it had been able to prevent the rebellions from taking place that would weaken its power in OTL, it may have been able to prevent Manchus from invading the rest of China. In OTL, the Manchu successes had much to do with internal Ming instability and was even aided by one of the Chinese rebels.
So, if Ming China proves stronger and more resilient in the face of the Manchu challenge, it may even have had the chance not just to fight back the last great nomads armies, but to defeat them and/or incorporate Manchu people/territories into its empire. Were that to take place, the best solution to keeping imperial stability would be to turn the Manchus energies and armies outward, to conquer lands to the west instead of allowing them to settle in Chinese lands proper. Given the effectiveness and discipline of the Manchu armies, it would have been possible to expect military successes and land conquests around 1640s from the armies that are led by Manchu cavalry, followed by Chinese infantry.
What would have been the effect on the rest of Eurasia at that time as the strong, imperial neo-Ming armies enter present-day Central Asia and start engaging the local tribes, threaten rich trading kingdoms, pose a challenge to the Persian Empirial influence and possibly make military contact with the Russian Empire that istelf was projecting its power eastward, towards Pacific? Thoughts?