Here I examine three "golden ages" for various regions that happened around the same time, only to collapse around the same time for various reasons. The challenge is to find a way for any of them, or even all of them, to continue on or at least last much longer and not go away as catastrophically.
1. The Tang Dynasty. Often considered China's golden age, marked by splendor, extravagance, and expansive borders going all the way to Central Asia. Now, this is actually the one I'm least familiar with here so I'd need a lot of help with that. Basically, the idea is to have the Tang dynasty last longer and not just crumble. Any political reforms needed to change things is okay. I'd even allow a change of dynasty if necessary as long as the other dynasty takes over quickly without losing much or any land and is also Han, so as not to alienate everyone like the Yuan and Qing. The whole idea is to preserve the culture and technological progress and all that. A bonus would be to have Taoism become more important than Confucianism, if not replace it entirely. Because Taoism is cool.
2. India. Before the Muslim invasions India was doing pretty damned excellent, what with being the richest place in the world and all. My idea here was to actually have the kingdoms unite to the point where ultimately India is mostly ruled by two Hindu kingdoms, one in the north and one in the south. The north Indian nation would rule all the land referred to as "Aryavarta" in the epics, and possibly use Sanskrit as a national/unifying language, or at least have a similar status and widespreadness as Latin in the West. The best choice I see would be to have the Gurjara-Pratiharas doing all that, as the ruler already did proclaim himself at one point as the Maharaja of Aryavarta. Most, if not all of the land in the south would likewise be unified, probably under the Chola Empire, ruled from either Thanjavur or Gangaikonda Cholapuram. This is a particularly fun one as they had colonies and vassals all around the Bay of Bengal, even in Indonesia.
3. My area of expertise, Mesoamerica. Some aspects of this I've already covered in my TL, the Maya do have an extensive history that makes this easier for them. On the other hand, I also include Mexico here. Averting the Collapse of the Classic Period shouldn't be too hard, there were various reasons for it and I've thought up various solutions already, some of them would have to be spread to Mexico and vice-versa. The problem however is Teotihuacan. They are the big superpower of the region, more powerful even than Tenochtitlan. Hell, Tikal's ruling dynasty was installed by them and traced their lineage to a Teotihuacano prince. Unfortunately we know nothing about the city itself, or at least very, very little. Even their ethnic identity is a mystery, I want to say Nahua but that's probably not true at all.
Anyway, what would be your guys' solutions to averting any or all of these collapses? What are possible consequences of any or all these scenarios happening? All of them happening is particularly interesting.