When you marry, it becomes a legal contract. So, to end your marriage, you must go through the legal process of divorce. As with any legal process, there are specific requirements you must meet to be eligible to file for a divorce.
FindLaw explains how each state has its own requirements for divorce. Some states have a list of things, but Missouri is fairly minimal in what it requires to qualify to file for divorce.
One of the most common requirements in every state is a residency requirement. To file in Missouri, you or your spouse must have lived in the state at least 90 days prior to filing your divorce petition. If you do not meet this requirement, you can wait out the 90 days or you can seek a divorce in the state where you do have residency established.
Missouri is a no-fault state, which means that you do not have to prove any grounds for your divorce, but you will need to show the court that your marriage is irretrievably broken. The court has the right to deny the divorce and instead give you a legal separation if it believes there is a chance to fix the marriage.
This could happen if your spouse is trying to avoid divorce or otherwise objecting to the fact that you cannot save the marriage. The court will need to consider all facts. It can help if you can prove traditional grounds, such as abuse or adultery, which may sway the court to make the determination your marriage is over and you qualify for a divorce.