Military ranks are military grades that depend on the "hierarchical organization" of the military.
To increase your military rank, you must gain ranking points, which you can get by 
- Defeating troops of other commanders on your server. If the enemy's command center is of a lower level than your own, you will only get a few ranking points. (This only applies to enemies on your server.).
- Killing troops of other commanders on the opponent server in the Cross-Server Border War event will get you many ranking points.
- Defeating troops from any server in the rebel warehouses.