Center
Though killing may not be forbidden inside the war zone, it was certainly frowned upon!
There was no need to needlessly kill because it was important to maintain a good relationship with all the races.
This would prevent multiple races from establishing an alliance to overthrow the other races and annex the broken world.
In the end, this was not needed by most common races because they had several areas with a similarly dense amount of mana, and it was only the war zone and other similar facilities that drew their younger generation to the broken world.
It was rare for some races to encounter other races as some liked to keep to themselves.
For such races, the broken world was exactly what they needed to get to know the strength of other races, and their prodigies!