Even in the most peaceful times, there were battles, especially if the participants were monsters.
Monsters had a huge number of reasons to fight each other, and sometimes it went beyond 1 on 1 combat.
It required a really good reason. Quite often, monsters could start fighting in a massacre format, where everyone was against everyone and either the strongest or the luckiest survived.
However, much more rarely, another event happened - one group of monsters fought against another. Sometimes it was Nest vs Nest, and sometimes it was just random monsters working together against another group of monsters.
Right now, a mixed version was happening in front of Adam and Katrin's eyes, as the huge flaming monsters had a clear goal of destroying the Igno Ants Nest.