What triggered the creation of the rank system in the US military?

The US military seems to have the largest amount of ranks for enlistment of any military. Specifically, in the Army there are 9 ranks in the enlisted ranks, NCO ranks, and officer ranks. You go up 9 ranks from being an enlisted personnel to an NCO, and NCO to Officer (Although, it can be different if you go through the academy). The ranks go up so quickly, and to make it worse, rank is everything. Specifically, in the Army, you are forbidden from associating with anyone rank above or below you unless you are a rank above another person, and even then you are discouraged from making friends with NCOs or officers if you are enlisted. It makes me wonder how this came to be.