The almost constant wars among the Sumerian city-states for 2000 years helped to develop the military technology and techniques of Sumer to a high level. The first war recorded was between Lagash and Umma in ca. 2525 BC on a stele called the Stele of Vultures. It shows the king of Lagash leading a Sumerian army consisting mostly of infantry. The infantrymen carried spears, wore copper helmets and carried leather or wicker shields. The spearmen are shown arranged in what resembles the phalanx formation, which requires training and discipline; this implies that the Sumerians may have made use of professional soldiers.

The Sumerian military used carts harnessed to onagers. These early chariots functioned less effectively in combat than did later designs, and some have suggested that these chariots served primarily as transports, though the crew carried battle-axes and lances. The Sumerian chariot comprised a four or two-wheeled device manned by a crew of two and harnessed to four onagers. The cart was composed of a woven basket and the wheels had a solid three-piece design.

Sumerian cities were surrounded by defensive walls. The Sumerians engaged in siege warfare between their cities, but the mudbrick walls failed to deter some foes.