There's a very cold-blooded but good reason why a nation rationally should use men as cannon fodder before women: they are more expendable in terms of reproduction. You need fewer men relative to women. Also, societies with more men than women tend to be unstable and high-crime and whatnot. Societies with more women than men survive a bit better.

> Also, societies with more men than women tend to be unstable and high-crime and whatnot. Societies with more women than men survive a bit better.

Demonstrably false: China and Russia