Men and women chugged along just fine in their roles for the last 20,000 years or so (or earlier if you want to consider our evolutionary ancestors along the homo genus line). When and why does gender role and identity confusion come about?
This happens when the expectations of the role and identity no longer accord with "tradition". It is arguable what tradition really means, but if we go back to our evolutionary roots, males and females perform particular biological functions, and it all then branches out from there. While this may seem somewhat deterministic, it is the very basis of how we got to where we are. Tough luck.
Our gender identities are then a subsequent product of these biological functions. By the roll of nature's dice (which isn't actually all that random), mammalian females tend to be the more selective sex while mammalian males have to compete for access to the sexual resources provided by conspecific females (of course this pattern is moderated by all sorts of other environmental factors, such as sex ratio and the social status of males, but the general pattern holds true). Therefore, women have traditionally been bestowed nurturing and homely roles, while men have traditionally been expected to go out and bring home the bacon, so to speak. Females often are expected to be coy and charm the males when on the mating market, and then expected to spend a larger of proportion of time than males taking care of children. All of this, in general and on average, of course.
Fast-forward then to the world of today. The proliferation of gender studies associated with the female identity is certainly an offshoot of the changing expectations on females. The modern, urban, and professional world is increasingly a world that blurs the divide between men and women. The more that people are obliged, compelled, or attracted to work in big multinational companies and take up professional working roles, the more that people have to behave.... well, like men. Simply put, the competitive world out there is a world that men have traditionally populated. Whether men created the rules of the game or not, it's pretty much a masculine environment.
This picture pretty much sums a lot of things up:
Although veiled behind the issue of physical attractiveness, females constantly struggle with expectations (and their associated effects with self-esteem) as a consequence of standards that are varied and often contradictory. Is she supposed to be submissive or strong? Is she supposed to stay home or work? Contemporary expectations of females do not make it easy. On the other hand, the male role tends to be very specific, and has remained stable relative to the female role. In short, for men, often there is no issue. Either you fit (good for you), or you don't (better buck up, or lose the benefits associated with being manly).
As we move along, if expectations on the male identity become more complicated (as is starting to happen now with the expansion of stereotypes of men), we can also expect to see an associated boom in the number of studies and attention accorded to the male identity crisis.