There were many significant political changes which Diocletian enacted. One important thing which happened was that he divided the Roman empire into two parts. This meant Rome was being effectively taken care of by two different emperors at the time for that reason.
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.
The steam locomotive allowed for the transportation of goods at a much more rapid rate than by horse. The railroad let people know exactly where and when goods would arrive. The trains also gave the cargo a safer ride as it was much more difficult to rob a train than a horse drawn transport. As more railroads were built, products could travel farther than ever before in a timely manner. This brought down the cost of freight transport and increased profits for many businesses.
