But like other people already hinted at you: the book about Haile Selassi was mainly a attack on his corrupt system back at home. By examining the power mechanisms and corruption of King Selassis court(and publishing it step by step) he managed to publish a antiauthorian criticism on corrupted buerocracy in general, in such a corrupted system. But he could do so, because when critizized from above he said: "Do you want to imply, that this corrupt monarchist court is comparable to our democratic peoples republic elected comitees?"
Which they could not admit, even though they understood how it was meant, because yes, they were just as corrupt. Unchecked power works the same in a monarchy, than it does in socialism or anywhere else.
He simply hated corruption and opression and he lived voluntarily among the poorest of the planet, to write about their lives and their struggles.