Starts at level 40.

There are 15 cities you need to try to take. The generals in each city are "geared" towards where you should be power wise for your level. So if you race up the leveling but don't work on keeping your power there to match, you will quickly get outclassed and only be able to take 8 or so cities.

When you beat a general you can try to recruit them, if it fails you can "buy" them for 2 gold. These generals are only there for the war game, you don't get to keep them when you go back out the world map.

The more you beat throughout the war game, the more chances you get to win Mount Spirit points to try to get new mounts (see mounts thread here for more details on them).

So there is an advantage to not driving up your general level and be strong power wise for as long as you can here.