Reinforcements can turn the tide of a battle. If an army of a faction is standing near another of the same faction, they get pulled into the battle to reinforce the other army, and get an advantage over the enemy faction you are facing. The next log will be about the captured settlement screen.
This is a screen from turn 195, where an army of the Haltmanns, lead by one Josiah Cook, have attacked a Squeak Army near a bridge. However, they brought reinforcements, lead by Susie, which put the Squeaks at a disadvantage. Both of the first armies have their faction leader (Josiah and Rick). New Units revealed: Haltmanian Gunner: A gunner with reversed colours, can shoot enemy targets as a ranged unit.