Could something like world war 1 happen again?

Answer 1

The war between Iraq and Iran from 1980-88 was somewhat similar in many respects. Neither side could gain an advantage, and the poor bastards in the trenches were ordered to go running at the enemy where he was dug in with machine guns, because the relatively unsophisticated command on both sides could think of nothing better to do.

But most western nations have progressed beyond the state of affairs in WWI. Air power is much more effective, and could obliterate troops in their trenches today. Amphibious attacks could be made to outflank the enemy positions from the sea. Tanks are much more effective than the pioneering prototypes developed in response to the conditions of WWI, and could today accomplish what their inventors dreamed of - smashing breakthroughs. "Vertical envelopment" by dropping paratroopers behind enemy lines is now possible, and was thought of in WWI but no one had the equipment to make it possible.

World War One was probably only possible on the scale it reached at that time and in those places. Which is not to say in any future war involving large numbers of nations that even more people will not be killed even faster. The evolution of military arts means the ability to destroy the enemy more efficiently.