the tie that binds

The value, belief, characteristic, etc., that is shared between or among people and which results in a unique and unbreakable connection. Usually used plurally. In our community, the welfare of our children has always been the tie that binds our families together. This national holiday is a celebration of our culture, our national spirit, and all the ties that bind us as a people. I know, the ties that bind can make it hard to go against your family on an issue like this.