You can gain Carange through Non-Arena PvP with players in other civilizations. When you gain enough Carnage you can learn powerful talents. Battling players within your Civ will result in only 1/3 of the normal amount of Carnage.
Recruit -0 Carnage Required
Private - 24,000 Carnage Required
Sergeant - 40,000 Carnage Required (Where you get to learn your first set of Talents)
Master Sergeant - 70,000 Carnage Required.
Captain - 115,000 Carnage Required
Cavalier - 175,000 Carnage Required (Where you learn your second set of Talents)
Cavalier Captain - 250,000 Carnage Required
Brigadier General - 340,000 Carnage Required
Lieutenant - 445,000 Carnage Required (Third set of talents)
General - 565,000 Carnage Required
Supreme Commander - 700,000 Carnage Required
Commander in Chief - 850,000 (Final set of Talents)
Carnage gain per unit killed
T1 pelt: 0.1
T1 pike: 0.1
T1 archer: 0.1
T1 cavalry: 0.1
T1 crossbow: 0.1
T1 trebuchet: 0.1
T2 pelt: 0.2
T2 pike: 0.2
T2 archer: 0.3
T2 cavalry: 0.3
T2 crossbow: 0.3
T2 trebuchet: 0.3
T3 pelt: 0.3
T3 pike: 0.4
T3 archer: 0.4
T3 cavalry: 0.5
T3 crossbow: 0.5
T3 trebuchet: 0.6
T4 pelt: 0.4
T4 pike: 0.5
T4 archer: 0.5
T4 cavalry: 0.6
T4 crossbow: 0.6
T4 trebuchet: 0.7
Armored Knight: 0.9
Gladiator: 0.9
Chariot: 1.2
Anubis: 1.0
Chu-Ko-Nu: 1.2
Mangudai: 0.9
War Elephant: 1.2
Muslim Cavaliers: 0.8