Best long riddles

I drift forever with the current down these long canals they've made. Tame, yet wild, I run elusive, multitasking to your aid. Before I came, the world was darker. Colder, sometimes, rougher, true. But though I might make living easy, I'm good at killing people too.

A horse is tied to a fifteen-foot rope and there is a bale of hay 25 feet away from him. The horse however is still able to eat from the hay. How is this possible?

Die without me, Never thank me. Walk right through me, Never feel me. Always watching, Never speaking. Always lurking, Never seen.

What country is hidden in the paragraph below? As defendants, we deny all involvement in the unscrupulous dealings which have come to light in the recent government investigation.

You just bought a cute rabbit at a pet store. The rabbit can breed once every month, and deliver 7 babies at a time. How many rabbits do you have after 12 months?

Only one color, but not one size. Stuck at the bottom, yet I easily fly. Present in sun, but not in rain. Doing no harm, and feeling no pain. What Am I?

I heard of an invading, vanquishing army sweeping across the land, liquid-quick; conquering everything, quelling resistance. With it came darkness, dimming the light. Humans hid in their houses, while outside spears pierced, shattering stones walls. Uncountable soldiers smashed into the ground, but each elicited life as he died. When the army had vanished, advancing northward, the land was gree and growing, refresh.

We travelled the sea far and wide. At one time, two of my sailors were standing on opposite sides of the ship. One was looking west and the other one east. And at the same time, they could see each other clearly. How can that be possible?

A little pool with two layers of wall around it. One white and soft and the other dark and hard, amidst a light brown grassy lawn with an outline of a green grass. What am I?

When Manish was three years old he carved a nail into his favorite tree to mark his height. Six years later at age nine, Manish returned to see how much higher the nail was. If the tree grew by five centimeters each year, how much higher would the nail be.