REPUBLIC TO EMPIRE is a Napoleonic rules set by Barry Hilton and partners. The general impression I've gotten from reading forums and blogs is that people think the rules are complicated. The game play is smooth and free flowing with minimal need to refer to the main text once concepts have been mastered. New players usually pick up the key mechanisms within three to four game turns.
As I do not own a copy of that I had to transfer everything to a rules set based on my Black Powder rules which I own. I simply love all the tips and hints in the bock about how to base or how many miniatures to base at once etc...
The difference is that Black Powder is scaleable to fit each scale. I own 28mm but could also use Black Powder on 20, 25, 15, 6 or whatever scale.