I'll chime in in support of this. It needs to at least do at least as well as Victoria 2, which did a great job of showing you at least part of the military side of the cost of war, naturally in game, through your efforts to fight the war.

I played vicky2 as a kid before learning much about WW1, played Austria, got into a great war and decided I'd hold off one front then turn around and attack the other. I had something like 20 groups of 10 regiments, so 600,000 men, in the assault army. They won, and I turned the armies around to support the other, now collapsing front, only to realize that my neat stacks had been ruined. Despite winning their front, the stacks of 10 were now stacks of odd numbers, with many regiments having been completely obliterated. The ones that survived were severely undermanned or being fed from pops that no longer existed in great enough numbers to replenish them.

Victoria 2 was the only game I had played that ever really drove home how costly Great Power wars were, and it didn't even touch on civilian losses or give any sort of event pop up, it just visually played out in the degradation of my army and the pops that made it up.