How do the states work together to preserve the union?

Is this for 10th grade if so I put the way the states work together to preserve the union by finally putting away there differences and let the states decide themselves kind of like that by singing the paper(sorry can't spell it) that had it where the state had represented and by the pop of the state is how many reps. They can have I hope u get what I'm saying I did this last week and I got a10/10 I did not use these words I can't remember what I really used but that sums it up hope this helps