War should be defined as a crime to increase accountability of those who choose it.
In general, one is not sentenced for a crime they did to avoid a far bigger loss or any way they were forced into it. Least force.
We need to put a stop to the meme that war is a fact of life and should be allowed to continue without questioning deep into the events every time. If the court is not convinced everyone leading the war on any side could not have avoided it, then they would be sentenced. At least 1 leader must have started it and must be sentenced for every war, or more if they all could have avoided it.
This will only work if most countries agree to it at once, similar to how you can't shrink or enlarge the military budge of one without the others following. This should be a global action.