A player can add other players as allies in two ways:
- By entering their Friend Code on the "Your Allies" page
- By paying the cost to hire them from the "Hire Allies" page.
Having more allies allows you to use use more of your lieutenants, weapons, gear, and vehicles in war with another player. There is a limit to the number of allies that helps in this way. By default, the limit is 500, such that you can take 100 lieutenants (1 per 5 allies), 501 weapons, 501 pieces of gear, and 501 vehicles into battle. Sin and Cesar both increase this limit.
A player can have no more than 1,500 total allies (apparently this limit can be exceeded if somebody adds you with your Friend Code when you're already at the limit).
Gifts can only be sent to allies.
Reaching 500 allies opens up the Underboss lieutenant seat.
There are Achievements that can be earned for gaining allies.