Why did the world war 1 last longer than expected?

Answer 1

World War I was expected to last little because European armies were used to fighting per the traditional method of infantry and cavalry, by which soldiers were limited to using traditional weapons like rifles and bayonets. When one fights a war like this, the overall "fighting" doesn't last long because soldiers run out of ammo relatively quickly and proceed to fight at close range with bayonets, and continue to do so until one side surrenders, thus ending the battle and, after a few of these, the war itself.

However, by 1914 (when World War I began), European armies had began to use machine guns, which were capable of taking down most of the incoming soldiers before they had the chance to engage in close combat. Since both opposing armies had machine guns and had approximately the same amount of soldiers, fighting the traditional way would have been entirely suicidal, as both sides would be immediately eliminated before even reaching each other. Therefore, each side dug trenches to defend themselves from incoming machine gun fire, and attempted to raid the other side's trenches, thus advancing towards victory. However, actually reaching the opposing side's trenches was almost impossible because of the constant threat of machine gun fire, so the overall battle took almost "for ever" to win.