by swheelock
You should go here:http://www.daysofwonder.com/memoir44/en/content/army-packs/
On each of the army packs' pages, you'll find a 'Rules' link where you can download the rulebook. The abilities/differences of the individual nations can be found there.
The Card Compendium is a good way to do it, too. Click on the 'Nation Cards' section.