Raid

A raid is an offensive move by a faction designed to disrupt and weaken your empire. Raiders are attracted to easy targets where they can inflict the most damage like resource buildings and unwalled or underfed forts, bridges and cities.

Raiders are generally cautious and will avoid areas that have large garrisons nearby. To deter raiders garrison units near valuable targets such as farms and active mines. Raiders generally prefer to avoid open combat and will often retreat if faced with equal or superior forces.

The likelihood of a (normal, non-raider) faction launching a raid against you is also determined by that faction's hostility. Factions with relatively low hostility might only send raiding parties into areas with multiple valuable targets such as full mines or undefended cities. Very hostile factions will be more aggressive and might launch a raid just to burn a single farm.