For what reasons was World War 1 so destructive?

Answer 1

One reason was the advances made in weapons.

Artillery had been dramatically improved over the previous forty years. Artillery used to be a line-of-sight weapon. It had to be up with the foot soldiers and the artillerymen had to see what they were shooting at. If they could see what they were shooting at, what they were shooting at could also see them, and shoot back. Now artillery was powerful and reliable. These new cannon could fire at, and hit, targets miles away. A forward observer with a field telephone could call back to correct their aim. There were new powerful explosives to fill the shells, and accurate, reliable fuses to explode the shells when they were supposed to explode. All this was new. Each side had vast numbers of cannon behind their lines, to pound the enemy.

Every soldier now had a modern rifle. These were high powered weapons, with a range of up to a mile. They were extremely accurate, and lethal. A soldier had to work the bolt to reload after each shot, but a trained man in the British Army could fire 120 shots, aimed shots, per minute - two every second. Mostly they did not shoot that fast, but they could if they had to. In the earlier wars, such as the Napoleonic Wars or the American Civil War, a trained man did well to get off three shots per minute. The range of the old weapons was less. The old weapons fired black powder, and soon put a thick cloud over the battlefield, and it was hard to see anything to shoot at through the smoke. The new rifles used "smokeless" powder. And, the new weapons were rifles, not muskets. This meant they were far more accurate and had a much greater range.

Machine guns had been invented. These allowed defenders to mow down attacking troops in rows.

There was all this new weaponry, but the generals were old. Military thinking tends to be conservative - the innovators get in lots of trouble. If it was good enough for Napoleon, by God, its good enough for me. So the tactics the generals tried were the old ones, and got men slaughtered by the hundreds of thousands, when they went running at the enemy, who had accurate rifles, and machine guns. The WWI generals never learned.

Because both sides had these types of weapons, the defense was strongest. Thus, neither side could break through the enemy lines in any big way. But the generals kept trying, because they could think of nothing better to try.