There is strong support in the population. It’s easy and cheap for Polania troops to reinforce their lines. Polania units are generally lighter and faster than others, but lack armor.
The Rusviet army is huge. Units are cheap and numerous. In close combat, it’s almost impossible to stop them. Rusviet forces are not that well equipped.
Saxony uses the most advanced technology with its strong long-range capabilities. They are reasonably fast and well armored, but expensive.