What group brought much of the Eurasian landmass under a single rule creating the largest landmass in history?

The Mongols around the 13th century

The first contributor is correct. Additional information displays the steps and extent of the Mongol Empire:

A. Between 1206 & 1227 AD Genghis Khan rules the Mongol empire;

B. Also during this period, the Mongols battle for and succeed in conquering northern China;

C. During this same period of time, the Persian empire is conquered by the Mongols;

D. By 1241 the Mongols have added parts of Russia to their empire;

E. By the middle of the 13th century, the Mongols capture Baghdad; and

F. The Mongol conquests were indeed, due to their ferocity and dedication to warfare.