Until 100 years ago there was no civil marriage in my country and no civil laws regarding marriage, it was just some penal law punishing polygamy. Then the state took ownership of the notion of marriage by regulating it by law and forbidding churches to perform marriage ceremonies unless you get married by the state, so the religious marriage is just a ceremony with no legal implications these days.
So yes, the state stole the term. It's like tomorrow the state decides by law that everything that color red will be called color blue, that would be stealing the word "blue" and use it to define the color of red things. It is not a natural evolution of language.
Yes, there was a time then marriage exist before religion, but it was not regulated by the state. The evolution would be unregulated->church->state. I think the unregulated and church ones are very close in term of legal implications (almost none), while the state is severely intervening and basically destroyed it in recent years.
So yes, the state stole the term. It's like tomorrow the state decides by law that everything that color red will be called color blue, that would be stealing the word "blue" and use it to define the color of red things. It is not a natural evolution of language.