Answer
One cause and effect relationship associated with the historical developments in documents 1 and 2 is the emergence of the Mongol Empire as a result of the leadership of Genghis Khan. Document 1 describes how Genghis Khan united various tribes and clans under his rule, leading to the formation of the Mongol Empire. Document 2 further explains how the Mongol Empire expanded under the leadership of Genghis Khan's successors, resulting in the largest contiguous empire in history. The cause of Genghis Khan's leadership and unification of tribes led to the effect of the emergence and expansion of the Mongol Empire.