Which group used the stirrup, skilled horsemanship, and siege warfare techniques to conquer much of asia and part of europe in the 12th and 13th centuries? (1) japanese (3) persians (2) vikings (4) mongols

The correct answer here is (4) Mongols. 

The Mongols were a nomadic people who travelled on horseback and were very proficient archers. They were said to be able to shoot a target from full horseback speed with their bows. 

They were led by Genghis Khan and conquered a good portion of Asia and also entered parts of Europe. Their empire was one of the biggest ones to date.