Women have been in support and combat positions in war since antiquity. Women buried with weapons were found in Kazakhstan in antiquity, otherwise quite a few Chinese armies had women in infantry positions (most often manning defences). See : https://en.m.wikipedia.org/wiki/Women_in_ancient_warfare

This generally doesn't happen unless either the society is quite rich but lacks strong men, or cases of emergency, or if there is surplus of land and food, because raising armies is very costly, and as a result it doesn't make sense not to send the strongest fighters possible as it is expensive to outfit them and to maintain production at home.

Nowadays, women are proving extremely competent as fighter pilots as their bodies are better at withstanding G-Forces, but in classical infantry where there is a large strength requirement again it doesn't make much sense.