In order for a marriage to be annulled, the marriage must be void or voidable. A void marriage never had legal effect. A voidable marriage exists but can be undone with decree of annulment. The legal effect of a decree of annulment is that the marriage is void.
While a divorce in Nevada is based on incompatibility, or separation for over one year or insanity existing for two years prior to the commencement of the action, the legal grounds for annulment are narrower and are based on the idea that a marriage is a contract. Like a contract, a marriage can be void depending on the facts. If the facts of the case do not fit within the annulment grounds, the parties should seek divorce and not annulment.