in 2015, I asked How can a planet-spanning empire keep their soldiers experienced without wars to fight?. After doing some more thinking and mental worldbuilding based on the answers to that question, I'm currently considering having specially assigned Warzones. Literal zones hundreds of square miles in size marked on the map are explicitly designed to have actual war, but instead of 2 nations warring against each other, it's the army of the world nation split into 2 parts.
Weapons are adapted so they only work in these zones unless otherwise needed, but apart from that, everything is just as lethal as in a regular, non-organized war, and both sides are encouraged to seek out new tactics and find any edge they can get. There is an agreement that interference between the world outside the warzone and the armies inside the warzone is kept to an absolute minimum, so no usage of weapons inside the warzone that may cause collateral damage outside the warzone; and no demoralizing the other faction's army by attacking civilians outside the warzone.
It's not a perpetual war: every 10 years, there is one organized war lasting 6 months, but during that period, the nation is in war mode, including all the consequences to civilians outside the war zone like rationing, conscription, war bonds, war economy,...
I'm not sure how this idea would work. Is it viable as it currently is? Is it viable if I change some of the numbers or details around? Does it have implementation problems that can be fixed by somewhat redesigning the war? Or are there fundamental flaws with the idea itself that prevent it from ever being viable?