Hey there, name's Reece. I've been reading some of these threads and have a good amount of answers for most of your non-technical problems.

Battling:
All things are measured in units. To destroy an enemy, you need to add up their amount of units and send more at them.

Dragons:
Dragons count as 20 units. That being said, it requires 20 level 1 swordsmen to defeat a single dragon.

Dragon Crystal Craters:
10 = 1 dragon
20 = 1 dragon
30 = 2 dragons
50 = 3 dragons
100+ = 6 dragons

Taking neutral cities (owned by local warlords):
First off, have as many units as they do. Second, the walls and tower count as units. So you need an extra 150 units to take it over.