Important external events—for example, divorce, a beneficiary's death, or the sale of property—may significantly affect how property is distributed under a will.
One big (and common) event is divorce. If someone wrote a will, and later got divorced but didn't make a new will, it can drastically change the person's estate plan in ways that may not have been anticipated.
In most states, if someone gets divorced after making a will, any gifts that the will makes to the former spouse are automatically revoked. For example, California law (Probate Code § 6122) states that:
"Unless the will expressly provides otherwise, if after executing a will the testator's marriage is dissolved or annulled, the dissolution or annulment revokes … any disposition or appointment of property made by the will to the former spouse."
If a gift to a former spouse is revoked by state law, who gets the property? The property passes as though the former spouse had died before the will-maker. So if the will names an alternate (contingent) beneficiary for that gift, that person inherits. If no alternate beneficiary is named, but the will names a "residuary beneficiary," then that beneficiary inherits. If the will doesn't name a residuary beneficiary, the property passes under state law, as if there were no will, to the closest surviving relatives.
For example, say that while Maria and Ernest are married, they make simple wills, leaving all their property to each other and naming their young daughter as the alternate beneficiary. Later, they divorce. The provisions in their wills leaving property to each other are void; if one dies before making a new will, everything will go to their daughter.
In some states, gifts to relatives of the former spouse are also revoked by divorce. (For example, see Ariz. Rev. Stat. § 14-2804.). If your state has such a law and, for example, a will leaves property to a former spouse's child, divorce would revoke the gift to the child.
If a gift to a former spouse is voided by divorce, the rest of the will is not affected; all the terms are still valid.
Divorce usually also revokes the appointment of a former spouse to serve as executor of the will or trustee of a trust. The alternate executor, if one was named in the will, would serve instead. If the will didn't name an alternate executor, the probate court would appoint someone, following the preferences set out in state law.
If the death occurred while the couple was seeking a divorce but still married, in most states the gift to the soon-to-be-former spouse would still be valid—even though that's probably not what the deceased person would have wanted. If the couple were permanently separated, however, that might be enough to revoke the will.
And if the divorce goes through but the former spouses have second thoughts and remarry each other, the old will is back in force.
If you're dealing with a former spouse who claims a right to inherit, you'd be wise to get an opinion from an experienced probate lawyer. There may be a way to settle the dispute without the high cost and bad feelings of a court fight.