What Am I Riddles

Question: A trail, a union, together tied.
Come across me and you will find,
you cannot change the course I'm on,
without me you cannot travel on.

What am I?

Question: I only point in one direction,
but I guide people around the world.

What am I?

Question: You can play me and pull me,
I love the naive.
I'm enjoyable to give,
but bad to receive.

What am I?

Question: Resurrected, they descend by the millions. Sometimes, to nourish and give life. Other times, to take lives or destroy. They have been known to fill entire valleys and block roads only to disappear before executing their long journey back to the top. What are they?

Question: Drop me and the world will shatter,
and you can always find me where you empty your bladder.

What am I?