Case in point. In international law there is a principle called comity. Comity, basically, is “legal courtesy.” In other words, a court in one country will not do anything to demean or denigrate the laws of another country, and will respect them and apply them as far as possible. It would be great if there was a binding principle like this for politicians, too – but that's a separate entry. In 1895, the Supreme Court found that “[a] judgment affecting the status of persons, such as a decree confirming or dissolving a marriage, is recognized as valid in every country, unless contrary to the policy of its own law.” Hilton v. Guyot, 159 U.S. 113 (1895)
So let's say two people get legally married in their home country and then come here to the United States. The marriage isn't “registered” here. Many people mistakenly believe that they are not married under US law. But this is where comity will apply. Unless there is a strong reason not to recognize the marriage (say it is a child marriage, or it was forced, or was with a relative closer than a first cousin, or is polygamous) then ordinarily it will be recognized as a valid marriage in the United States. This means if the couple wants to get divorced, they will have to obtain a divorce from an American court, notwithstanding what they may do in their home country or in their own religious tradition.
But just because the marriage is recognized, it is far from clear as to what extent: many marriage contracts have clauses for dowry, bride price, deferred bride price, property clauses, etc. and many disgruntled spouses try to enforce (or deny) such provisions when they obtain a divorce in the US. It's rarely clear, without a full-fledged legal analysis, whether an American court will enforce these provisions or refuse to do so.
If marriage laws vary, then divorce laws are literally all over the map. Even among our united States, divorce laws are discordant. And if you're talking about a divorce from overseas, it becomes even more murky.
Because bigamy is a crime that can have very unpleasant consequences – especially for noncitizens, couples in the US whose current or previous marriages or divorces were outside the United States would do well to consult with an attorney to determine which documents would be valid, and if there is any “overlap.” (Overlap being an innocuous-sounding term for being married to more than one person at the same time.) And just because a divorce is valid in one country does not mean it will be valid here!” Comity will not save in every case.
As the Court of Special Appeals of Maryland has found, “[t]he principle of comity, however, has several important exceptions and qualifications. A decree of divorce will not be recognized by comity where it was obtained by a procedure which denies due process of law in the real sense of the term, or was obtained by fraud, or where the divorce offends the public policy of the state in which recognition is sought . . .” Wolff v. Wolff, 40 Md. App. 168, 389 (1978)
Bottom line: before you tell the government you're married, make sure you really are. Before you tell the government you were married, make sure you still aren't. And before you think your foreign marriage contract lets you keep your million dollar real estate empire, be sure to run it by a competent divorce attorney, who may tell you, “May be cheaper to keep her.”