Why did infantry attacks across No Man's Land cause so many casualties?

Infantry attacks across No Man's Land during World War I resulted in catastrophic casualties primarily because defensive technology had far outpaced offensive tactics.1

The primary factors contributing to these losses included:

• Dominance of Defensive Weaponry: The introduction of machine guns and rapid-fire artillery created a "storm of steel" that made open-terrain movement suicidal. Defenders, often protected in trench systems reinforced with barbed wire, could easily repel exposed infantry.1
• Rigid Formations: Commanders often ordered troops to advance in dense, symmetrical waves. This lack of tactical flexibility made soldiers easy targets, as seen during the First Battle of the Somme, where troops were described as being like "ninepins" waiting to be knocked over.2
• Logistical Burdens: Soldiers were heavily laden with equipment—often over 60 pounds—which restricted their movement to a slow walk, preventing them from crossing No Man's Land quickly enough to reach enemy parapets before defenders could react.2
• Failure of Surprise: Prolonged artillery bombardments often failed to destroy well-entrenched defenses and served only to alert the enemy, allowing them to bring up reserves to close gaps in their lines.23