The Yuan Dynasty (1271–1368) was founded by Kublai Khan, the grandson of Genghis Khan, after he defeated the Song Dynasty in the south. It marked the first time all of China was ruled by a foreign power — the Mongols. The dynasty was crucial in unifying China, expanding trade (especially via the Silk Road), and promoting cultural and technological exchange across Eurasia. Major achievements include the improvement of the Grand Canal, postal system, and welcoming foreign visitors like Marco Polo.