Suppose we have two groups. Group A believes that women are human beings, just like men are, and that they should be equal partners in their society. Group B believes that women were created by the devil to tempt men, that they have no human rights, and that they must be used to have as many children as possible. If Group A and B live in different parts of the world, each region will develop in a way that reflects their different ways of life.
The higher birth rate enjoyed by Group B will make it more aggressive, particularly since a society that devalues women will also cull baby girls and practice polygamy leading to a surplus of young male. But those same qualities will also help keep it backward, making it much less effective militarily against a modern productive and efficient society. Group B will therefore have a great deal of trouble successfully invading Group A's territory, unless Group A allows it to happen. That of course is the situation we're faced with today.
There are a number of approaches that would balance the demographic scales between Group A and punish Group B.
For example, Group A might refuse to share the advanced medical technology that its society develops with Group B, unless the latter agrees to enact certain reforms that will grant rights to women and help lower the birth rate. If it agrees Group B will have a more stable and less threatening society. If it refuses, its high birth retain will have to compete with a high death rate. However if Group A provides Group B with the benefits of its medical technology, without demanding social reforms as the price-- then Group B will pose even more of a threat, because its population boom will continue for ideological, rather than biological reasons, no longer to compensate for a high death rate, but on purely competitive grounds.
Group B will begin suffering from a population surplus, which it will try to export into the territory of Group A, by force or immigration, collectively or individually. Group A will now begin experiencing demographic competition on its own soil. If like so many empires throughout history, it sees them as a beneficial form of cheap labor that will help keep its own citizens prosperous by making the cost of goods and services cheaper, it will have eventually doomed itself through demographic suicide.
By reaping the benefits of Group A's social setup, without accommodating itself to those same parameters, Group B is engaging in social parasitism, partaking only of the advantages to themselves, while avoiding their natural consequences. Much the same as a welfare recipient benefits from a social safety not paid for by active workers, exploits a system without paying into it-- Group B exploits Group A's social setup that it cannot recreate on its own.
Alternatively Group A might prevent Group B from settling in its territory. This would force Group B to live with the consequences of its ideology. Group B would be allowed to fail, and have the chance to learn from that failure, and enact reforms for a more stable society. Forcibly attempting to invade Group A's territory, would show Group B its own impotence, and force it to contemplate the causes of that impotence. It will probably not draw the right conclusions, much as the Arabs in the aftermath of several lost wars, decided the solution was not a civilized society, but to replace Arab Socialism with Islamism. But they will have the time locked up in their own territory to contemplate and to change. They will have examples of what to become and what not to become.
So long as there is distance, both groups can live with the consequences of their social setups. However once Group B migrates into the territory of Group A, so long as Group A tolerates it-- it only needs to compete on demographics. And not on anything else. No matter what else Group A achieves, it will eventually be outnumbered by Group B. The resulting society will have the values and laws of Group B, unless Group A tries to maintain a tyranny. Even this will not avail it in the long run, as tyrannies must mimic the values of their subjects to be effective. If they fail, they will be toppled. So if Group A does nothing to change the terms of the competition, it is hopelessly doomed.
As a result Group A keeps trying to cooperate with Group B, which instead of cooperating takes but doesn't give, thereby destabilizing the social setup. If Group A continues to tolerate such behavior, members of Group A will try to begin joining Group B, to protect themselves or to gain advantages in the competition for resources. While members of Group A cannot be part of Group B's primary nexus of loyalty, they can become part of its secondary nexus of loyalty. Within Group B, people who are protected by the secondary nexus, but are not blood kin, have a second class status. But within Group A, those who are members of Group A already hold third class status, because they have obligations to Group B, which has none to them. Since ordinary Group A citizens have become third class, those who are even part of Group B's secondary nexus of loyalty are already a step ahead of them in the shifting landscape of the country.
Since Group A's society is cooperation based, it will try to accommodate Group B. However since Group B's society is authoritarian based, it will refuse to accommodate Group A. The less clearly Group A insists on reciprocity in its social contract, the less Group B will cooperate with it, since it does not cooperate without gain for its nexus of primary loyalty. Group B's rejection of interoperability cripples it socially, but not demographically. Group A's openness enhances its skills, creativity and knowledge; but dooms it in the demographic competition. While Group A thinks that the net result of their interaction will be Group AB, Group B thinks that the net result will be Group BB. And while Group B is not entirely right, Group is entirely wrong, because while Group B will be influenced by Group A, it will still absorb it.
Group A allows itself to be defeated by failing to meaningfully leverage its strengths, instead relying on a social and political model that is no longer relevant to the problem it faces. That is because like most societies and cultures, it has a blind spot when it comes to its own weaknesses, either refusing to recognize them, or insisting that they are actually strengths. Group B is doing the same thing, but by exploiting Group A, it has actually managed to take its greatest weakness and turn it into a limited strength. Group A has no one to exploit but itself. Its own system insures that its limited attempt to exploit Group B will cost it, more than it will cost Group B.
Like many cultures, the self-images of Group A and Group B vacillate between omnipotence and impotence. In the omnipotent state of mind, the group believes that it is invulnerable and destined to succeed. In the impotent state, it believes that it is doomed and completely incapable of doing anything to change that. This cultural form of manic depressive thinking can actually lead from one to the other. Both however are misguided and dangerous. A culture which feels that it has hit bottom, may rebound with a sense of false omnipotence by seizing on an old or new idea to reinvigorate its identity. And a culture which is cloaked in its own sense of omnipotence may be unwilling and incapable of recognizing how bad things have gotten, only to sink into impotence when it does. In this scenario Group A is suffering from impotence, while Group B is experiencing omnipotence. And few in either group understand how quickly the tables can be turned. But a cultural rebound can be just as destructive, because desperate people will seize on anything that offers them hope, without thinking it through. And hope without reason can be a very dangerous thing.