Other gangs can challenge your control over an Underworld, leading to an Underworld War. These wars are fought with a weighted point system: wins provide up to 10 points and kills up to 20, depending on the level differences between players. This means strategy matters just as much as brute strength.
An Underworld War lasts for one hour, and if the defending gang successfully resists, they keep the Underworld. Gangs holding multiple Underworlds may have to defend them simultaneously, making coordination and preparation even more critical.