This world has been used as a sort of buffer, a hub of sorts between universes. They come and they go and they shop and they fight here. It's used for this purpose because of the ways that the universes collided
The universes here have not converged into one universe of its own, the universes here have collided into one space. That space being the city where this all takes place
At first this led to conflict... However... As more powerful universes collided, advocacy and diplomacy took a much bigger stage, allowing for negotiations between the universes instead of conflict
The people of the universes were able to come together and talk to each other. Bring their own technological advancements from their civilizations. This is how this society was taken out of its dark ages into an industrial revolution
However, the aggression that all of the species that came failed to be satiated by this era of peace. Which is why this civilization decided to take inspiration from the humans. ...One of these inspirations, surprisingly was the sport of boxing. Welcome... To the future of boxing.