I have a question related to ethics laws

My husband has worked for an employer for 3 years and 2 1/2 years has been verbally abused by his regional manager. I mean, to the point where he spews profanity and called him horrible names etc. In January, he was called into his manager's office and was not only cussed out twice, but he was humiliated in front of the other staff members in the office. After this meeting was over, he asked his direct manager if he thought this it was appropriate for the regional manager to speak to him like that and he agreed that it was not. My husband explained to him that if he spoke to a stranger like that out in the street, that there would probably be a fight. He was fired for making terroistic threats...is this legal? I understand other employees filed complaints with HR and nothing was done.