In every civilization you can name, in every place and time through history, marriage has always been a legal contract that was recognized by the state/nation/whatever it was.

That's a mighty big statement. Would be really interesting to see actual evidence but seriously..... no.

Nations are fairly recent creations in the evolution of society, the 'state' also.

I'd be willing to bet that in the vast majority of cases, it was NOT some sort of legal recognition, but rather, a religious and social convention that was embedded in the community life, far more than it was ever 'legal' - except perhaps for the very, very minority group of aristocrats and royalty.