What factor made it difficult for either side to win World War 1?

Answer 1

Warfare continually evolves and at the time of WWI developments had made the defensive much more powerful than the offensive. Defenders with machine guns, rapid firing, bolt action rifles with magazines holding several rounds of ammunition, and rapid firing artillery - which for the first time in a large war no longer had to be a "line of sight" weapon (meaning artillerymen did not have to be able to see what they were shooting at) all gave great power to the defense. This defensive power was multiplied when the defenders were dug in to prepared defensive lines. Since both sides had these weapons, and both sides were dug in, neither side found it easy to attack successfully and break through the enemy line. Even on the rare occasions when a breakthrough was achieved, exploitation of that breach in the enemy line often proved impossible other than for very moderate local gains. This was because the troops achieving the breakthrough would be exhausted and hungry, their ranks severely thinned by losses in the attack. All food, all water, all resupply of ammunition, all reinforcements had to be brought forward over the shell blasted and cratered no-man's-land, over the remains of barbed wire entanglements and the multiple huge ditches of trenches criss-crossing the battlefield for miles, all pulled by horses which found this terrain impossible to traverse at anything other than a crawl.