It made it harder for the countries to achieve unity.
One example for this is the separate existence of Chile and Argentina - they are separate counties, because they are separated by the Andes.
Generally, natural borders, such as rivers and jungles made the political unity harder.
I would explain, but since you had the mind to post numerous questions, I only have time to give you the answers. Sorry about that.
1. C
2. C
3. C
4. D
5. A
<span>6. B</span>
Magnetic Force? I think aha. Almost positive.