The phalanx was a military formation created by the Athenian army that was very efficient because the soldiers overlapped shields and moved together as a unit in a way that made it almost impossible for them to be hit.
The Phalanx was a factor of Athenian democracy because it made possible for all people to join the military before its invention one needed to have money to buy a horse. With the phalanx, all people could join the army, and people from less prosperous families could join the army, which made the military more “democratic”.