I once read a sci-fi book where a team of humans colonized a planet that had a few huge river monsters living in the water. The colonists encountered the monsters while fishing and were afraid of them, so they killed all of the huge monsters. Shortly after that, a massive wave of smaller monsters stormed their camp. It turned out that the river monster was the mature form of the fish they had been catching. Without the mature river monster keeping them in check, many of the smaller fish were turning into monsters.
We like to think of ourselves as being the colonists in this case. The reality is that after the World Wars we decided it was more important to be the big river monster.