I realize this is an old thread but the information from the reply is incorrect. Marriage was originally a contract for wealthy white men to protect their property. I'm sure you remember from studying history about women having dowries. Women and children were thought of as property at the time.
This was done for many different reasons. It was to ensure alliances, binding powerful families together, and strengthening weaker families. It helped people survive in the barbaric era of early humanity. It was also to ensure that a mans children were biologically his. The female children were the mans property which he would bargain off to strengthen the power of his family while the male children would work and bring in money, also strengthening the family. Marriage existed long before Christianity existed, therefore it was created by man for survival purposes.
Religion was not originally interested in marriage until they found they could make money from it to help pay for their expenses. The bible "says" nothing about marriage - what they bible is "talking about" is the rite of holy matrimony and that is not a right, but a religious concept. It is a rite of passage like birth, puberty ceremonies, betrothal, matrimony and death.
What the OP is asking is more complicated and can be looked at in more than one way. Religions were originally created to create structure in society, before there were governments. Governments were created later but usually merged in with religion...to some extent....and can even be seen today... (see some of the most messed up places on the planet)
The Christian religion created Holy Matrimony. Marriage was always a civil institution. At some point, Christianity did take (some) ownership of it, but really, it was never theirs to have. But then again, the same can be said for Christmas (winter solstice/noel), Easter (spring equinox), etc.