Wars of the Diadochi
After reaching its zenith in the conquests of Alexander the Great, the phalanx began a slow decline, as Macedonian successor states declined. The combined arms tactics used by Alexander and his father were gradually replaced by a return to the simpler frontal charge tactics of the hoplite phalanx. The expense of the supporting arms and cavalry, and the widespread use of mercenaries, caused the Diadochi to rely on phalanx vs. phalanx tactics during the Wars of the Diadochi.