Why most of the Deserts are located at the Western margin of any country?

Deserts are generally located on the western margins of continents because of the prevailing wind patterns and ocean currents.

 The trade winds bring moist air from the ocean to the eastern side of the continents, causing precipitation and leaving the western side dry. Additionally, the prevailing winds and ocean currents can cause the western margins to be warmed by air that has traveled over the warm ocean, causing low humidity and high evaporation rates.