The answer is Erosion, which is the the gradual destruction or diminution of something -- in this case, rocks. I hope this helps! For reference/perspective, sand is the product of rock erosion, because it's really just tiny remnants of crushed rock. Those "small pebbles" could be sand, but you'd have to emphasize just how small they are -- one grain of sand is just that: a grain
The African Americans helped out the war majorly throughout that time period. They participated in protest marches and also tried to join the forces with blacks to fight for freedom.
The protestant reformation divided western Christianity though it has been divided before
Separation of powers ensures a relatively fair government because no branch is given too much power. This system is called a "checks and balances" system, in which each branch relies in part on the others.
