The number one reason marriages end in divorce is because people don't choose wisely. They don't spend enough time knowing each other before they get married or do the due diligence that one might do on a car.
Everything stems from that. If you haven't worked out in advance how money is going to be spent or who is going to work, finances are going to be a problem. If you are not on the same page about in-laws, children, or goals, you're setting yourself up for failure. Religious and cultural differences, which don't seem like a problem when you're dating, suddenly become a huge issue later, particularly when you have kids.
If you don't practice communicating before you get married, you won't communicate when you are married. There won't be trust because you haven't built a foundation for it. Your spouse will become your enemy instead of your compatriot, and resentments and arguments will take the place of needs being met.
Divorces are largely a result of grossly insufficient maturity and preparation. You need to really get to know the person you're marrying so as a couple, you don't bring insecurity, mistrust, hostility, and anger into the marriage.