You prove that your marriage ended by providing:
A certified copy of the divorce decree;
A certified copy of the annulment decree; or
A certified copy of the death certificate (or other proof of death, see §1720).
If none of the above is available, you can submit any other evidence of investigative value. You must explain why none of the items above is available.
If your prior marriage ended by a divorce in a State that imposes a restriction on remarriage, you must show that your remarriage does not violate the restriction.