On the right is an army summary screen. Units with medals fight better, and most units can be upgraded when new technology arrives. Combined arms, of light and heavy infantry, cavalry and artillery, come into play significantly, especially when assaulting a fort, where infantry can be used to draw opportunity fire before nimble horse artillery can be brought to bear on defensive cannon. One snag here is that green is used to indicate fit troops, and on a green background, it's hard to tell regiments who are about to rout from those who can still fight. This is more notable when fighting against level 3 forts, which are very tough nuts.
Most battles result in only a few regiments lost, with survivors fleeing to fight another day.
In general, this is very enjoyable, and feels relatively original. Diplomacy is one failing, in some ways. While you can, most admirably, influence nations by trade, alliances can be a snag. You can ally with a nation to fight a common enemy, that nation can make peace with your common enemy, but you end up left at war with it, dunked into a conflict you'd rather not be in. This makes your choice of allies an important one.