How did Kublai Khan, Marco Polo, and Zheng He help to open China up to the rest of the world?
Kublai Khan and Marco Polo encouraged trade along the Silk Road that opened up China to rest of the world. Zheng He failed in that his sea explorations were abandoned by the Chinese.
The Mongal Empire reached from China to Eastern Europe, the Middle East, and India. Kublai Khan as the Mongolian ruler of China encouraged trade along the ancient silk road. Kublai Khan as a foreigner to China himself was not xenophobic as common in the history of China. Kublai Khan wanted people from the rest of the world to come to China for trade.
Marco Polo was one of those foreigners that came across the silk road during the time of Kublai Khan. Marco Polo wrote a book about his experiences in China that inspired others in Europe to want to trade with China.
Zheng He was a great navigator. His fleet of ships sailed all over the Pacific and Indian Oceans. He visited numerous countries opening these nations up to trade with China. Chinese pottery has even been found in Mexico. Sadly on Zheng He's return to China the rulers of China decreed that the rest of the world had nothing to offer China. Zheng He's fleet was burned and his logs about his travel and trade were also burned.