The natural order mandates that certain creatures form groups (packs, colonies, herds, etc.); and man is one such creature. Normally this system functions as a method of ensuring the success of a species, allowing for more efficient predation and/or defense, as well as reproduction. Animals that form groups are generally territorial, particularly predators, and will chase away, fight, or even kill, members from a different pack (naturally, exceptions are often made for fertile females). Checks and balances present in nature guarantee that these species are just successful enough. Group size is governed by both available resources and overcrowding; a crowd may simply be two equally dominant individuals: a bee hive will only have one queen, a chimpanzee troop will only contain one dominant male.
Man has taken his pack mentality to an extreme, and has created a seemingly infinite number of divisions within humanity; with the added complication of grouping people into numerous overlapping categories. We will set aside aspects of the two ends of the spectrum for now, and look at general clan classifications.
Family units are basic, and natural; providing for the safety of animals that are born with undeveloped survival skills. Human infants require years of care before they gain the ability to fend for themselves. To ensure this care, pair bonds are established using a reward system: sexual reward for the male, and security for the female. . Extended family units are the typical primate groups; these are generally patriarchal, and genetic diversity is accomplished through capturing or enticing non-related females into the group. In nature, this is as far as it goes for primates; but one primate, man, has taken it considerably further.
Mankind groups by religion, political affiliation, geographical region, race, gender, class, recreational pursuit, age, and by any other detectable difference. The most damaging to harmony within the human race is nationalism. Grouping people together because of imaginary lines drawn on a map is based on territorial instinct. Protecting or enlarging one's territory is typical animal behavior; however, the scale of confrontation is considerably less in nature. The entire political system that drives nationalism is in place because the vast majority of people have no interest in managing the infrastructure necessary to make our technological world function. A relatively small number of individuals manage society as proxies for the masses, and direct world events from a perspective that is quite alien to most people. A large portion of humanity now lives a parasitic existence; they are incapable of existing without the "host" society. In a totally natural environment, these people could not provide for the basic needs of shelter and sustenance, nor could they provide themselves with clothing, nor successfully give birth to and raise infants without outside intervention. Much of their knowledge is restricted to what they are told by politicians and the media, and their opinions are carefully molded to serve whatever is in the best interests of the elite.
The people who are in control: politicians, the rich and powerful; are primarily motivated by animal drives. The quest for material gain, power, and prestige, is simply the way human males subconsciously manifest sexual competition: to demonstrate that they are the dominant, and therefore most suitable, of mates. It is no different from primitive man dragging home the largest animal carcass. This behavioral trait applies to all men, and is deemed competitive spirit. The emergence of women, in the normally male dominated arena, is a socioeconomic phenomenon, and is not instinctive: females compete in nature, but not to this extreme.
Fundamentally, there are no significant differences between forms of government. It doesn't matter whether a system is Capitalist, Communist, Monarchist, or any other type; all have a ruling class which manages the masses. It is advantageous for aggressive nations to cultivate a fear in the general population of governments that are dissimilar, for this enables the elite to manipulate the people into supporting actions, detrimental to those other nations, that they would otherwise perceive as immoral. In theory, politicians are supposed to act in response to the wishes of the citizens; but in reality, the leaders act in their own interests, and then create a favourable response from the people through media manipulation.
Leaders of nations frequently provoke warfare for purely economic or political reasons. A war between countries requires that a significant number of citizens are easily brainwashed: from the soldiers who must be willing to kill strangers, and be killed themselves, for something they do not understand; to the general public, which must support the ideal of murdering others for gain. In reality, all the standard excuses countries use to defend acts of aggression do not justify slaughtering people who have done you no wrong. War against another nation is perceived as a war against that state, as an entity unto itself; but a state is composed of the individuals inhabiting that area: women, children, the elderly, the poor, the handicapped; people you would normally treat with compassion.
Countries assume the identity of the majority of citizens: they are a representation of the type of people living in that region. Theocratic governments function as religious entities, and tend to enforce laws and enact policies according to sectarian doctrine (example: Iran). A theocracy in conflict with another nation risks having the religion, rather than the state, seen as the enemy; this situation can easily escalate, as other nations that share the same religion feel obligated to defend/support their beliefs.
Countries that are predominantly of one race tend to develop a cultural identity, and often view other races with distrust. Humans, like other animals, are suspicious of any creature different from themselves; this is based on instinctive fear, and fear frequently breeds aggression. Obviously, there are other factors involved in racism. There are also exceptions to the rule, where a racial minority governs; but these situations are the result of conquering forces maintaining control, and are temporary: the masses will eventually supplant the rulers.
Bias due to race, culture, or status, is not logical for a species that wishes to rise above animal instinct. Fear or mistrust of the unfamiliar serves to protect animals from danger; but man is an intelligent creature, and can determine the level of risk through reasoning. There is no compelling reason to assume that a member of a different group would pose more of a danger than any other individual; but man is a victim, of not only instinct, but the sum of millions of years of conditioning. The attitudes held by society shape each and every individual within it. Most information a person acquires is filtered through others; everything taught in school is not necessarily the truth, but is what society perceives as the truth. Centuries ago, science held that the universe revolved around the Earth; this was truth because all knowledge at the time established this to be so. Human knowledge evolves slowly, with the influences of each member affecting the flow of change; each person altering society to varying degrees, for better or worse. An apparent sudden alteration of human culture by an individual is not as it seems; for the actions of that person are the culmination of two million years of genetic and behavioral events, all leading to that one point in time. Humanity, as a whole, is the result of the actions of every person that has ever lived; and is in a state of constant, gradual transition: but transition that is confined by limits set by instinct. The animal drives are a major reason why new knowledge does not necessarily lead to widespread change. The realization that followers of Animistic religions did not have magical powers may have stopped witch burning, but religious persecution continues. Science has shown that the differences between races are superficial, but racism continues. Man is a creature of habit; enlightenment will take time.