This is something I have thought a lot about recently -
Is it the permission slip obtained from the government?
Is it found in the permissions to have sex granted through religious rites which are conducted?
Is it the people involved?
Is it all of those things?
When I got married we did not wander into the nearest government office and obtain a permission slip to do so - which I suppose means we are not "legally married." Not being "legally married" does not prevent us from being married... it merely prevents us from taking advantage of the governmental benefits one acquires when one is "legally married."
We did not go searching for the nearest Jewish-Catholic-Buddhist-Protestant-Muslim-Shaman-High Priestess either... We were united "Between Mother Earth and Father Sky" in the way our people have gotten married since before the arrival of the first European on the continent.
Before "Christians" arrived to "civilize" us we were united between Mother Earth and Father Sky in the eyes of Wakan Tanka. That is the way my husband and I chose to get married and we are just as married as someone who possesses a permission slip from the government. You see, we know that marriage is much more than a piece of paper. Marriage is much more than sex, much more than children, much more than feelings.
Marriage is what happens when we remember there is more to "US" than there is to "ME"...