Several years ago, José became a US citizen, but he was still not married. He said that he couldn't find a good woman in America, so José went to México, married Juanita, and had a big wedding reception at Juanita's village.
José went to the US consulate in Guadalajara, filled out several papers, and waited a few months. His wife, Juanita, came to the US four months later.
Mario came to the US and married an American citizen. After Mario became a US citizen, he divorced his American wife and became involved in drug shipments from Latin America.
The US Attorney could not get Mario for drug trafficking, but he got Mario for bigamy. The US Attorney prosecuted Mario because he had been married in Colombia, and without divorcing his Colombian wife, he moved to America and married an American.
Mario said he had been separated from his Colombian wife even before he came to America, and he thought that foreign marriages did not count in America. He was convicted of bigamy.
Real life examples.
Jacques and Pierre achieved wedded bliss in Montreal, they moved to Colorad. Voila, they are not married in the eyes of Colorado or the US of A.
But I don't understand your point. The states are bound by the Constitution through full faith and credit. Treaties made with other nations, are Constitutional but a whole other ball of wax. No relation to each other.