What Was the Apparent Motivation for the Turco-Mongolian Warlord Named

What was the apparent motivation for the Turco-Mongolian warlord named Timur-lenk (or Tamarlane) to conquer vast areas of land?

A) He sought to enrich his personal wealth.
B) He wanted to gain personal fame.
C) He want to keep his army engaged in combat.
D) He did it just for the sake of conquest.
E) He wanted to accumulate large numbers of slaves.