#42

A descendant of the Turkish plunderer Timur on his father's side, and Genghis Khan on his mother's side, X was born in Ferghana, and became its king at the age of 12. X coveted the magnificent city of Samarqand but was never able to retain it for any substantial period of time. He even lost his home kingdom of Ferghana in the bargain. He later on crossed the Hindukush and became the ruler of Kabul, where his attention turned to the "Land of Dust and Diamonds", Y. He mounted an invasion of Y in 1526, during which he received a mocking letter by the Shah of Persia, calling him a Z, meaning "descendant of the Mongols". However X took it as a mark of honour, and formally adopted Z as the name of his clan. X went on to rule large sections of Y, and his descendants took his legacy forward. Ironically enough the last direct descendants of X were all brutally executed in the mid 19th century by the W. Some surviving descendants live in considerable poverty.

Simple.
What are X,Y,Z,W?