I'd never heard of M. J. Engh before, but bought Arslan (first published in 1976) because it had an arresting cover and was published as part of the Gollancz SF Masterworks series. It's a powerful and unsettling novel - I was glad the extreme brutality of the opening chapter didn't continue throughout the book, although violence and conflict are never far away.
The premise is an odd one, but is carried through with confidence. Arslan, a general from `Turkistan', becomes the leader of a Soviet backed coup in which the US's defences are disabled, allowing Arslan to take control of America. He makes the small town of Kraftsville his headquarters, and we, together with the citizens of Kraftsville, gradually learn more about his plans, which are partly driven by a (very dark) green agenda, and a wish to return humanity to a more self-sufficient way of life.
Arslan is compared with Tamburlaine, and the novel, like Marlowe's play, is morally disorienting, and made me wonder quite how we were meant to respond to its ruthless but charismatic central character and his radical environmentalist agenda. It's a really astonishing novel, and fully worthy of its place in the Masterworks series. However the second half is not quite as compelling as the first.