I doubt that there is any one main reason for a divorce. Some are for legitimate reasons such as; cheating, abuse (physically, emotionally and substance).
Then you have other reason. They get married and when something does not go there way or they are just tired of the relationship, boom, divorce! Marriage doesn't mean anything to them.
Problems during would be the expense and the fighting. Cost of lawyers, Cost of losing things that mean something to you, to the other person, the constant fighting and hamstringing.
Problems to deal with after a divorce are learning to live with out an additional income, dealing with life alone, not have another person to lean or depend on.
But then again some divorces are very civilized and not all that dramatic. But most aren't. I personally have not been through one but have seen some nasty ones!