Why is the Sahara Desert so large?

The Sahara is the world’s largest hot desert because its climate is dominated by persistent high-pressure systems around 20° to 30° north latitude. In these belts, air sinks, warms, and becomes drier, which suppresses cloud formation and rainfall. The Sahara’s vast size is also influenced by the continents of North Africa, the Mediterranean, and the topography that limits the reach of moist air in some areas. Deserts can also expand and contract over long climate cycles, but the Sahara has remained arid for thousands of years.