It gets iffy, but the idea behind annulment in the Catholic Church is that the marriage was never valid in the first place.
Hence if there was no marriage form the beginning, there is no marriage now and there is no need for divorce (within the church, civil marriage falls under civil law) seeing as there is no marriage.
I know firsthand of a couple who have had an annulment within the Catholic Church on the basis that the groom was drunk on his wedding day, they were together for 15+ years and he was somewhat of an alcoholic throughout.
Nevertheless they had a two-year engagement leading up to the day of marriage, yet the Church deemed that the marriage was indeed invalid seeing as though he was intoxicated on the day of.
Sadly they have children together and it has been very hard on the children, and neither one of them are happy that they are divorced, and neither are looking to be remarried, yet they can’t seem to reconcile with each other, He has considerably cleaned up his act and now talks of becoming a lay brother.
This particular couple is the only couple I personally know so it is really the only example I can give, I will say that the sheer number of annulments within the Catholic Church today versus in years past is quite astounding and it sure does seem like it is a Catholic version of divorce, although in practice it shouldn’t be.