Monarchial system in europe was the major cause factor of first world war. How?

There were big empires and kingdoms and they started going against each other militarily.

answer; i had to look this up and the only one i found was(last only 15 minutes) plz check first and good luck;

industry had made the u.s. the richest nation in the world at this time. the second industrial revolution caused growth in industry and transportation, which allowed increased trade between nations.