Why do men abuse their spouse?

Many reasons: Limited insight and self-awareness coupled with low self esteem and often a history of abuse are often characteristics of abusers. Abusers tend to blame their victims but abuse is the result of something wrong with the abuser not the victim. Adherence to strong gender roles, presence of a toddler/teen in the home, holidays, and football are all stressors that increase chances of abusive episodoe.

Several reasons: When a sub-culture accepts that men should be more powerful than and control women, harming them to maintain control becomes acceptable. If violence was witnessed as a child, a man may believe it is ok. Some men believe that it is part of "being a man." if a man was traumatized by violence as a child, he may not have skills to manage anger or his own behavior. He could be mentally ill.

Power and control: Two excellent answers already. Abusers use physical and emotional violence and intimidation to keep the partner in a one down position. Exercising power is an emotional high that's addictive. Abuse masks the insecurity of the abuser who believes this is the only way to keep her. Attacking her self-worth is a standard tactic. The victim can break the cycle but only by escaping.