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Why did World War I battles often last weeks or months instead of hours or days?

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tactics Sumerian phalanx, a block of foot soldiers depicted standing shield-to-shield, presenting spears, and advancing in a dense mass, detail from the Stele of the Vultures, limestone bas-relief, c. 2450 bce; in the Louvre Museum, Paris.

World War I battles frequently lasted weeks or months because of a fundamental imbalance between defensive and offensive military capabilities. Advances in technology, such as machine guns, rapid-fire artillery, and barbed wire, gave the defense a massive advantage, forcing troops to dig into extensive trench systems for protection.123

Because these defensive positions were so strong, attackers struggled to achieve breakthroughs. When they did manage to penetrate a line, defenders could use rail and motor transport to quickly move reserves forward to seal the gap. Furthermore, the massive scale of these armies and the need for tremendous concentrations of artillery meant that offensives required extensive logistical support; when supply lines could not keep pace over devastated terrain, momentum was lost.425

As a result, the conflict on the Western Front settled into a static, prolonged stalemate where neither side could gain a decisive advantage, leading to battles of attrition that dragged on for months, such as the Battle of Verdun and the First Battle of the Somme.617