The attack system is very simple. Each army that attacks has a 60% chance at killing one defending army. If all of the defending armies are killed, the territory is captured and all the attacking armies move to occupy the destination territory.
For example, if you attack with 10, you will kill, on average, 6 armies. This is why you generally want to attack with at least twice as many armies as the defender has.
Defenders also get an opportunity to kill attacking armies. Each defending army has a 70% chance at killing one of the attacking armies. The defender's kill roll does not impact whether or not the territory is captured.
Generally, you always want to have overwhelming numbers in every battle you participate in. Clearly, however, this isn't always possible, so you must pick and choose your fights to make the most effective use of your armies.
In the animation shown in the upper-right right, 7 armies are shown attacking a territory defended by 4 armies. Note the left territory had 8 armies to start with, but it can only attack with 7 since one army must remain on all territories.
Each of the 7 attacking armies has a 60% chance at killing one defending army. Each of the 4 defending armies has a 70% chance at killing one of the attacking armies.
In this case, the attackers killed 4 and the defenders killed 3 (represented by the four checkmarks on the left and the three checkmarks on the right). Since all of the defending armies died, the territory is captured by the attacker. 7 armies were attacking, and 3 were killed by the defenders, leaving 4 to occupy the newly captured territory.
Let's say that 15 armies attack a territory that has 6 armies.
The attacking 15 armies could have killed between 0 and 15, but on average they will kill 9 (60% of 15). Let's say they kill 9 armies.
The defenders could kill between 0 and 6 of the attacking 15 armies, but on average they will kill 4 or 5 (70% of 6). Let's say they kill 5 armies.
5 of the attacking armies die and all 6 of the defending armies die. Since all the defenders died, the remaining 10 attacking armies take control of the defending territory.
Failed attack example
Let's say that 25 armies attack a territory that has 20 armies.
The attacking 25 armies could have killed between 0 and 25, but on average they will kill 15 (60% of 25). Let's say they kill 15 armies.
The defenders could kill between 0 and 20 of the attacking 25 armies, but on average they will kill 14 (70% of 20). Let's say they also kill 15 armies.
15 of the attacking armies die and 15 of the defending armies die. Since 5 defenders lived, the territory is not captured. The remaining 10 attacking armies retreat back to their territory of origin.
Within the game, Warzone supplies a tool called Analyze Graphs. These provide an easy way to determine the odds of attacks succeeding without needing to understand all of the math and logic presented on this page, and is a timesaving convenience for those that do.
Analysis of battles
Calculating how many armies will be killed can be done with the binomial probability formula. If we run this formula on 100 attacking armies, we get a bell curve like this:
We can see that the most likely number of armies that will be killed by 100 attacking armies is 60, which will happen about 8% of the time. The standard deviation is approximately 4.3465 armies. The number killed will thus be between 55 and 65 armies 75% of the time.
Settings that affect the attack system
The calculations on this page assume that the game's luck modifier is set to 100%. Most games use a lower value, which reduces the amount that randomness affects the game. To see how this changes the calculations, see the Luck Modifier.
As a sub-setting of the luck modifier, rounding mode also affects luck in the game, and as a result, the attack system.
Overridden kill rates
The default offense and defense kill rates are 60% and 70%, but these can be changed by game creators. Therefore, for multi-player games, it's a good idea to check the settings on your game to be sure.