Final answer:
Sea-walls had two significant effects on the Mongols: minimized interaction with maritime civilizations and forced them to adapt their military strategies.
Step-by-step explanation:
The effect of sea-walls on the Mongols was:
- Minimized their interaction with maritime civilizations.
- Forced them to adapt their military strategies.
The Mongols were experienced in land warfare but had little experience in naval warfare. The geography of southern China, with its extensive river systems, created obstacles for the Mongols' naval expansion and conquests. As a result, they had to rely on non-Mongol experts for naval warfare and adapt their military strategies to overcome these obstacles.