What changes did the Mongols bring to China

When the Mongols took over a place, they normally did not change their way of life. Their main goal was to conquer land. They had great religious tolerance, but they didn't know how to really control a government. Though when they took over China, which was divided into three states (Tanggut, Jin, & Song) they united these states. The merchant economy flourished. Technology also continued to advance.