Space

One view of life is in terms of space. We can say that all living things need space in which to exist in order to survive. How much space is required varies from species to species and even, in the case of man, from culture to culture. The amount of space required depends on how aggressive, that is to say masculine the species or culture is. A very masculine species, say a mountain lion, is a very singular creature, while a very feminine creature, say a Wildebeest, exists in large groups. In the same way, a very feminine culture, say the Chinese, live in very dense populations, while a very masculine one, say Americans live in very spacious areas. Within a large entity like a culture, great variance is to be expected, so that hermits and gangs will exist in any culture.
It is proper to say that the world is apparently, already full, and always is, except in unusual circumstances and when they arise, when the New World was discovered, for example, it will fill up as rapidly as possible.
Proximity is a crucial question. Entities of a very dissimilar nature cannot exist in close proximity. This is because one will either eat the other or, in the case of culturally distinct humans, they will compete for food. If they are sufficiently similar (having common parents in a small number of generations), they will be able to cooperate. Proximity is not a simple concept, since one can distance oneself from another entity by existing at a different scale, in which case a nearby entity may just be part of the environment and not a competitor for your space. Fleas, for example, don't compete with humans, though Black Widows might. If conflict arises, this informs us that space is the problem.
So, with these ideas in mind, what features of life can we explain?
There is a constant effort to find and exploit new space by all living things. It is inherent in living things, a basic feature of life. This is so because the more space is inhabited, the better the prospects for survival. This can be done in a variety of ways, the simplest of which is just to discover a compatible space not known before, thus migration. Another way is to adapt to a space by altering one's nature, birds learning to swim or fish learning to fly, for example. Humans devise new clothing. There is strong resistance to form alteration built in to all creatures but, I would speculate, under the right circumstances, it will be overridden. When the weather makes a permanent change, for example. It will be a very demanding experience, using all available energy for a while and producing the sensation of great sickness. But, if survived, a new creature will result.
In many cases new space will be very difficult to find or adapt to, so that a great motivating force is required to force a species to make the attempt. One motivating force is overpopulation. Another is environmental change that invalidates one's adaptation. Success is always problematic and death is the reward for failure, so that conservatism will require that one continue in the current space available and manage numbers to allow that state to continue. But, if one's predator disappears, overpopulation will inevitably result, and then death, migration, or adaptation must follow.
There is an inherent conflict here. One must needs destroy competitors for one's space, but, if too successful, then overpopulation will result, forcing a departure from one's current space, at least for the excess.
So, this will be the final reason for all wars, whatever the more proximate cause may be. Negotiation, as is currently popular, is really just another name for feminization, since higher density population is possible for a less aggressive species. This is also the reason for ghettoizing. If one's neighbors are all similar to oneself, greater density is possible, while when one's neighbors are different, in any respect, less density is possible. When too great density is reached the excess must emigrate or die.
Finally, this explains one of the most vexing problems with sex. Since sexual intercourse is the closest sort of coexistence, it requires that the partners be, or at least seem to be very similar. Should dissimilarity become apparent, rejection will soon follow, as a matter of self preservation instinct. Unhappily, people mature in a variety of ways sometimes producing very different results, so that, even though a couple are very similar at the point of marriage, social forces may cause them to mature in very different directions, for instance when one partner pursues immoral methods of making money. But that is just an obvious possibility. Not so obvious possibilities are the pursuit of religion, or excessive eating or drinking. This is, of course, deadly to the marriage, if one or both partners are pro sexual. Another reason this problem is so common, is the overconfidence of one or both partners at the point of marriage in their ability to adapt. Adaptation requires dogged perseverance over long periods of time and will not be possible for convenience. It amounts to emigration, which any immigrant can tell you is a problematic business.
This line of reasoning explains the great increase in divorce in Western civilization in this century. Feminism is opposite to masculinism, or Judeo/Christianity as it is known. As more and more people gravitate towards feminism while their spouses do not, or move more gradually, proximity rejection will set in. Happily, this will have the effect of decreasing the rate of population growth.