The reason that military forces tend to be composed mostly of men is for two very practical reasons:
1. Men are on average physically stronger than women, and at their peak are physically stronger than is possible for any woman. This is more useful in a combat situation.
2. Women's bodies are specialized for pregnancy and childbirth. Without women providing this essential function, the next generation of humanity would not exist. By contrast, men are more disposable because all they do is provide the sperm.
A society where almost all women have been killed in battle cannot effectively repopulate, as there is a bottleneck of pregnancy: it is a long process that - excluding relatively rare cases of multiple births - requires one woman per newborn to conduct. A society where almost all men have been killed can repopulate much more rapidly, as it only takes a small number of men to fulfil the male reproductive role of providing sperm.
In fact the existence of sperm banks makes the widespread obliteration of males even less of a risk to the survival of humanity. Plus there is a promising subfield of stem cell research on growing viable sperm from female cells, which would remove the reliance upon males entirely.
1. Men are on average physically stronger than women, and at their peak are physically stronger than is possible for any woman. This is more useful in a combat situation.
2. Women's bodies are specialized for pregnancy and childbirth. Without women providing this essential function, the next generation of humanity would not exist. By contrast, men are more disposable because all they do is provide the sperm.
A society where almost all women have been killed in battle cannot effectively repopulate, as there is a bottleneck of pregnancy: it is a long process that - excluding relatively rare cases of multiple births - requires one woman per newborn to conduct. A society where almost all men have been killed can repopulate much more rapidly, as it only takes a small number of men to fulfil the male reproductive role of providing sperm.
In fact the existence of sperm banks makes the widespread obliteration of males even less of a risk to the survival of humanity. Plus there is a promising subfield of stem cell research on growing viable sperm from female cells, which would remove the reliance upon males entirely.