Gender segregation
Gender segregation is the reservation of areas or organisations that exclude either men or women. A high proportion of human societies have chosen some form of gender segregation and it is one of the biggest criticisms westerners often level at non-western societies.
Until around 2015 the trend in Western nations was for men's spaces to be in decline and for women's spaces to be growing, producing one-sided gender segregation. This changed with the rise of the trans movement. From this point trans women generally had unrestricted access to women's spaces.
A lot of gender segregation in Western countries is being driven by feminists who state that they often feel threatened by men, sometimes merely by their presence.[1][2]
This raises the interesting question about whether it was women who drove segregation in other societies. This would be notable considering that gender segregation in non-western countries today is often claimed as principally disadvantaging women.
It may be reasonable for a society to permit gender segregation, but it must be on just and equal terms. Thus a society should permit both men's spaces and women's spaces only if they are available on equal terms. A society should allow both or it should allow neither. Until recently women in the West enjoyed uninterrupted access to women-only spaces and organisations while men were today largely prohibited from having men-only spaces and organisations. Since 2015 the rate at which trans women have successfully entered women's spaces has increased significiantly.