I am not an expert on Rastafarian theology, this question came to mind — embarrassingly — because today's featured article on Wikipedia is about Rastafarianism.
I believe that Haile Selassie was an Ethiopian Orthodox Christian and Rastas believe that he was (is?) God incarnate. That is a pretty plain violation of the First Commandment, the Nicene Creed and by my understanding the Second Commandment as well. How did he respond to this publicly and do we know (from diaries, recollections of others etc) how he felt privately, if those two things differ.
Further, in 1974 the communist Dergue took over Ethiopia and overthrew the monarchy, imprisoned the royal family and killed him, though they claimed he died of natural causes and the execution order wasn't confirmed until many years later. I can't imagine how horrific it would appear to someone for their living God to be dethroned, humiliated and murdered, wars and uprisings have been started over much less.
Your questions have been answered before.
u/Commustar, What is the relationship between Ethiopian emperor Haile Selassie I and the Rastafari movement in Jamaica?