Perhaps,
1. Build a Militia Training Grounds. This allows you to build Militia Units.
2. Militia Units cannot leave the city and cost less than normal units. Players can design their own militia units.
3. The number of militia units is limited by the population of a city and do not consume population. I.e. population 10 = 1 militia max, population 100 = 10 militia units max. Militia losses reduce the cities population. Example: Loss of 5 militia units reduces population of city by 5.
4. Militia units do not fight in the face of overwhelming odds (30 point militia unit faces 300 point army = militia unit doe not fight, 30 point militia vs 30 point darkling attackers = militia fights)
5. Militia units are activated only if there is a champion in the city to call them to action. This increases importance of recruiting champions.
6. You can only build experienced militia units or militia units in patrols or squads if there is a champion in the city to oversee the training when Militia units are purchased. This increases importance of recruiting champions.