The book is “Empires of Sand” I was surprised about how good it was. Hard to believe it was Ball's first novel. An interesting mix of historical fiction and rip-roaring adventure; informative and very well researched and written.
He has written two more after that I believe, but have not read them yet, so I can’t comment.
I decided to add it to the forum because of some similarities with WS novels. Two brothers separated for years by a conflict and then reunited fighting in opposite sides.