Given the rules you’re laying out - which I don’t necessarily have a problem with - it seems very difficult to make this calculation.

Can a given death be double-counted? Or we have to split it up, assigning fractional responsibility to various powers?

In major conflicts that have killed millions of people, there are usually many powers involved, sometimes dozens, to varying degrees.

What if I claimed that the threat posed by the Ottomans in the 15th century helped spur European colonialism around the world? This would mean I could plausibly assign every death in the Americas, Africa, and and Asia at the hands of Western powers - and at the hands of fellow colonized peoples in civil wars that resulted indirectly - to Turkey.

(Then again, the Poles and Hungarians were at war with the Ottomans before they conquered Constantinople, so perhaps Poland and Hungary are to blame for all “Western” deaths.)

Do you see why it’s nearly impossible to make these calculations using the rules you propose?