The steep gradient of the river have more or less energy of river?

The total energy that a river possesses varies from one stage to another because of changes in the river's height, gradient and speed. In the upper course where the gradient is steep and river is high above sea level,  the river has a high gravitational  potential energy.  In the middle course, the potential gravitational energy is converted to kinetic energy and the gradient begins to level out resulting in the river's velocity increasing.

By the time the river reaches its lower stage, it has no gravitational potential energy but lots of kinetic energy resulting in a high velocity. 

there's multiple reasons why the conquistadors were so successful in colonizing central america, and some of them are:

- they were seen as gods;

at the beginning, the spanish settlers were seen by the natives as gods, and this was mainly due to their white skin, and the way they came with their boats.

- possessed superior weaponry;

the spanish had gunpowder and guns, as well as cannons, while the natives did not had any fire weapons.

- made cleaver alliances;

they used the situation of tribes hating each other, so they made alliances with some of them which served them very well.

- brought diseases;

the native people were not immune to certain diseases the europeans brought with them, so they were dying from seeming harmless things for european standards.