Final answer:
Rivers and oceans are seen as barriers due to difficulties in navigation, natural separation between landmasses, and hindering interaction between people.
Step-by-step explanation:
Rivers and oceans are seen as barriers for several reasons. Firstly, they can be difficult to navigate and cross, which can limit travel and movement between landmasses. Additionally, they can form natural barriers between landmasses, separating people and cultures. Lastly, rivers and oceans may keep people apart that would otherwise interact, impacting trade and communication.
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