All the 50 states now have no fault divorce. What does that mean?
It means that in order to get a divorce, that you do not have to prove that one party to the marriage engaged in bad behavior and the other was innocent, in order to get a divorce.
However, getting a divorce is only part of the equation. You also need to address child custody, child support and parenting time, if you have children. Even if you don't have children, you need to address property and spousal support (alimony). In Michigan, fault still impacts child custody, property distribution and spousal support. I think the same is true in many other states.
Fault was generally defined as adultery, abandonment, abuse. It required one party to prove that the other party was guilty of "fault" and the other was innocent of any fault. A judge had to hear the evidence and determine whether there actually was fault and whether one party was guilty and one party was innocent. In my experience, most divorce cases occur because the parties have grown apart or were not very compatible in the first place. There is no clear cut fault. Most judges take the position, that if one person strayed from the marriage, meaning they had an affair, that the marriage was diseased and the affair was a symptom of the weakness of the marriage. Most judges do not believe that one person would have had the affair if there were not significant problems in the marriage. Judges often do not know what to do about abuse and about the inequity of power between the parties.
When one party comes to the divorce believing that he/she will have a decided advantage due to the bad behavior of their spouse, they are probably in for disappointment. In Michigan, judges may compensate for "fault" in property cases by awarding 55% of the property to the innocent spouse. They may enhance the spousal support, though they usually do not award a much more than they would absent fault. Fault can impact the award of child custody. However, many times, the court will order a psychological evaluation of the parents and base the custody award on what the psychologist recommends. The innocent party may not present significantly more healthy than the "at fault" spouse. In the case of adolescent children, they often want to maintain a relationship with both parents after the divorce.
In short, divorce happens because one party's needs are not being met by the marriage. There can be fault. However, it is more important for couples who are divorcing to look toward the future than to dwell in the past. The marriage is broken. It's good to know why that happened to permit you to have a healthy relationship in the future. But it does not change that a divorce will happen.