By the time the first Neanderthals reached Central Asia, maybe about 100,000 BC, most of Central Asia was covered by hundreds of miles of tall grass, like the prairies of South Dakota or Nebraska in North America. There were hardly any trees, and not much water. We call this grassland the steppe.
Further south, it was warmer, but there was still not enough water for farming, so people did not farm there. At first they hunted wild aurochs and horses, and gathered wild grain and apples and wild carrots and many related herbs – dill, parsley, caraway, cilantro, celery, etc. Later, when they had tamed horses to ride, people kept big herds of cattle, and rode horses like cowboys to watch their cattle. The steppe made it easy for people on horses to travel long distances very fast, so people used it as a kind of road to get from Europe and West Asia to China. Animals and plants also traveled across the steppes, so that many different kinds of plants grow there and animals live there.
The south-eastern part of Central Asia is too dry even for grass to grow there. It is the Gobi Desert. Mostly people don’t live in the Gobi Desert.
Because most of Central Asia is so far from any ocean, the oceans can’t help control its temperature, and it gets very cold in the winter and very hot in the summer. Even in the Gobi Desert, it gets way below freezing in the winter, though there’s not much snow because there’s no water. On the steppe, there may be several feet of snow in the winter, and then temperatures over 100 degrees Fahrenheit (40 Celsius) in the summer.
Nobody knows yet whether the Medieval Warm Period or the Little Ice Age affected Central Asia, but it seems likely. Possibly the warmer weather from about 800-1200 ADencouraged people to have more children and increased the number of people living in Central Asia: the Khitan, the Samanids, etc. Possibly, again, when the weather got much colder about 1200 AD, a lot of those people decided to leave and invaded West Asia and China, forming the Mongol Empire.