Final answer:
The enhanced sea-walls of the Great Wall presented a significant obstacle to the Mongols' invasion attempts, strengthening Chinese defense and contributing to China's stability and population growth.
Step-by-step explanation:
The sea-walls significantly impeded the Mongols' ability to invade China, bolstering the Chinese defense against these skilled conquerors. While Mongols excelled in siege warfare and built bridges to aid their mobility, the fortified Great Wall presented a formidable barrier.
The Great Wall's enhancements under the Ming Dynasty improved defense capabilities around key economic and political regions, hindering the Mongolian assaults and helping to safeguard China's population growth and territorial sovereignty.