Rare, not nonexistent. The World Wars are the main recent exception I was gesturing towards, although more extreme examples exist on a smaller scale: the Napoleonic Wars killed somewhere on the order of a third of French men eligible for recruitment, for example. And they were rarer before modern mass conscription, although exceptions did exist.
They are now, anyway.
The Ottoman Empire lost 13-15% of its total population in WWI but had by far the worst proportional losses of that war, particularly from disease and starvation.
In WWII, Poland lost 16%, the Soviet Union lost 13%, and Germany 8-10%..
In the U.S. Civil War, the U.S. as a whole lost 3% of its population, including 6% of white Northern males and 18% of white Southern males..
Rare, not nonexistent. The World Wars are the main recent exception I was gesturing towards, although more extreme examples exist on a smaller scale: the Napoleonic Wars killed somewhere on the order of a third of French men eligible for recruitment, for example. And they were rarer before modern mass conscription, although exceptions did exist.