Central Asia vs. central plains of US?

There are a number of reasons for this. Here are two major ones:

1) Asia is much larger. The centers of large continents, based on what we know of weather and climate patterns, tend to be more extreme in temperature and rather dry. (See also Africa and Australia.)

2) What really saves North America, though, is the Gulf of Mexico. Having a warm body of water coming from the windward side of the land (swirling clockwise up and out of the Gulf does it for N.A.) makes a huge difference. This is one reason large continents are more prone to deserts. It would be similar for Europe if Europe were further south.

Note that the desert areas of the U.S. start just west of the westernmost longitude line of the Gulf of Mexico.

Ultimately, it's all about wind directions and proximity to (especially) warm water sources.

Central Plains Usa

All the large natural deserts were not formed very recently, they exist at least for a million years back from now.

And your comparison is more peculiar. Do you find any other geographical similarities on the basis of North/East/South/West regions between these two continents? Then why only Central parts of these two compared by you? I do not think Asia and American continent posses similarities in terms of climate or weather or geography. But of course, any continent does posses at least a small desert, many rivers, few mountains and mountain ranges, islands, and so on.

For directly answering the second part of your question.

Why a large desert? This might have been due to various reasons and when it happened, it was massive in scale as well. Say large scale flooding of rivers, large scale flooding of water from oceans inland, extreme dry weather for a very longer period and so on and so forth.

I like Spister's answer but wish to add that the Himalaya Mnts block the warm, moist monsoon winds from reaching central Asia, allowing cold, arctic air to dominate the area. The resulting freezing helps to create desert conditions.

Remember, not all deserts are hot. Antarctica is, in effect, a desert.

The western United States also has it's share of areas that are practically uninhabited because of their desert like conditions. The area known as the badlands and most of west Texas is a good example. Death valley and the small but isolated deserts of the American southwest do not compare with the Sahara or the Gobi in size, but are just as deadly and forbidding.

The difference is the altitude. Central Asia is about 4000 feet higher than the central part of the U.S.