There is the tendency for some people to use the terms marriage and civil union interchangeable. They may look similar but they are not the same. Here are some of their aspects that make some difference.
The major difference between these types of unions or relationship is their level of acceptability. Marriage is generally accepted in all the cultures, tradition, states and nations of the world. There is no tribe or culture that does not recognize the institution of marriage even though, the ceremony and practice may differ from place to place. But this is not the situation with civil union. It is accepted only in few states or nations in the western world. In other words, the rights of couple into domestic union begin and ends in the states or country where it is allowed.
In the same vein, civil has no place in most religions of the world. But marriage is widely accepted by all religions of the world. Each religions has rituals or the way marriage is celebrated. But there is no rituals for civil in most religious. It is only contracted legally. Couples who are living together in civil union may be look upon with contempt in some major religion of the world.
Marriage and civil union can be dissolved. However, their method of dissolution are not the same. There are different ways of ending or dissolving a marriage depending on the stipulation of a country or state or religious requirements. The major ways of ending dissolving a marriage nowadays are annulment and divorce. These two terms are not the same and their legal requirements also differ. Marriage is annulled based on the fact that it has never existed ab initio. But in the case of divorce, there was marriage but owing to some problem it is being ended legally if the requirements for divorce are meet. Civil union can be dissolved but through annulment and divorce because it is not marriage. The requirements for dissolution of civil union should be stipulated in the constitution of the state or country that allows it. So, it is left for the couple to prove the ground for dissolution.
Marriage and civil unions conferred some rights to the couples that enter into them. However, the rights conferred on the couples by marriage is larger and widely recognized than the rights conferred on couples by civil union. The rights conferred by civil is only accepted in the state where it is practiced. For example, if you contracted a civil union in an American state where it is accepted and you are living in another country where it is not recognized, you will not make any claim to any of the right. But this is not the case in marriage. If you are married in America and you are living in the UK with your spouse, the rights conferred on married people in the UK still apply to you.
The above are some of the differences between marriage and civil union.