Most of the vital records kept in the US do not go back much further than 1900, but that does not mean some are not out there. There are all types of vital records that you can find when searching, including birth, death, marriage, and divorce. These can be helpful, as you have to prove that you are divorced when you want to remarry, but can also help you when you want to find out more about your family history. These can help with a dead end or to correct information already found.
There are a few reasons why divorce records are so important when you are tracing your family tree. Your ancestor may have married a few times, which can muddy the lines. You may not know through which husband or wife you should go. When the ancestor you seek is from a first marriage (which is often the case in past generations), you may not realize that without finding divorce records. You could search by the wrong last name, leading you to ancestors that are not really yours.
When you cannot find someone, divorce records can help because children can be listed on those records. That means this could be the only place where you find that child, and then the real father or mother. Family records tend to change with marriages, so that first marriage may not be listed where the last one would be. If you cannot find a name, look for those divorce records to see if there was an earlier marriage that helps you out.
You can find divorce records online where you find other types of vital records. You can use the search engines to search the name of someone along with the tag divorce or divorce records. You are going to get a variety of results. If you find that this name was listed on a genealogy site, this might be where you want to look initially. Those are generally where this information can be found first.
If you want to cut out a lot of time and dead ends when searching, you can always see what a paid service can do for you. These can find the records that you need to learn about past divorces that have an effect on the direction through which your family tree should go to be sure things are accurate.