Great powers are rarely in a position to pursue a full-scale liberal foreign policy. As long as two or more of them exist on the planet, they have little choice but to pay close attention to their position in the global balance of power and act according to the dictates of realism. Great powers of all persuasions care deeply about their survival, and there is always the danger in a bipolar or multipolar system that they will be attacked by another great power.

The key to understanding liberalism’s limits is to recognize its relationship with nationalism and realism.

The influence of nationalism often undercuts a liberal foreign policy. For example, nationalism places great emphasis on self-determination, which means that most countries will resist a liberal great power’s efforts to interfere in their domestic politics—which, of course, is what liberal hegemony is all about. These two isms also clash over individual rights. Liberals believe everyone has the same rights, regardless of which country they call home. Nationalism is a particularist ideology from top to bottom, which means it does not treat rights as inalienable. In practice, the vast majority of people around the globe do not care greatly about the rights of individuals in other countries. They are much more concerned about their fellow citizens’ rights, and even that commitment has limits.

Liberalism is also no match for realism. At its core, liberalism assumes that the individuals who make up any society sometimes have profound differences about what constitutes the good life, and these differences might lead them to try to kill each other. Thus a state is needed to keep the peace. But there is no world state to keep countries at bay when they have profound disagreements. The structure of the international system is anarchic, not hierarchic, which means that liberalism applied to international politics cannot work. Countries thus have little choice but to act according to balance-of-power logic if they hope to survive. There are special cases, however, where a country is so secure that it can take a break from realpolitik and pursue truly liberal policies. The results are almost always bad, largely because nationalism thwarts the liberal crusader.

are humans fundamentally social animals who strive hard to carve out room for their individuality, or are they individuals who form social contracts?

There is no question humans have an impressive capacity to reason. Still, this capacity has significant limits, especially when it comes to answering essential questions about what constitutes the good life. Almost everyone agrees that survival is the most important individual goal, because without it you cannot pursue any other goal. But beyond that, there is often intractable disagreement about the answers to the important ethical, moral, and political questions that all societies confront, and which have profound implications for daily life. Those differences over first principles sometimes become so passionate that they create the potential for deadly conflict.

humans are profoundly social beings. They do not operate as lone wolves but are born into social groups or societies that shape their identities well before they can assert their individualism.

With political institutions comes politics, which is crucial to daily life in any society. Politics is essentially about who gets to write the rules that govern the group. This responsibility matters greatly because the members of any society are certain to have some conflicting interests, as they will never completely agree about first principles. Given that basic fact of life, whichever faction writes and interprets the rules can do so in ways that serve its interests rather than its rivals’, or reflect its vision of society rather than its rivals’. Of course, power matters greatly in determining which faction wins this competition. The more resources an individual or faction possesses, the more likely it is to control the governing institutions. In short, in a world where reason takes you only so far, the balance of power usually decides who gets to write and enforce the rules. Given the absolute necessity of politics for the functioning of social groups, when I say that humans are naturally social beings, I am in effect saying they are also political beings. This obviously includes hunter-gatherers, who are sometimes wrongly portrayed as operating alone in a Hobbesian world. In fact, they lived together in small groups in which power, rules, and factions—that is, politics—were unavoidable. The political and social dimensions of the human condition go hand in hand. Questions about what constitutes the good life are axiomatically about political as well as social matters.

Politics is vitally important in the relations between self-governing social groups. There are no higher political institutions, however, that can write and reliably enforce rules that might govern their behavior toward each other. The power to write rules, which matters so much inside a society, thus matters much less at the intergroup level. Still, power itself matters greatly in dealings among groups, because possessing superior power allows a group to get its way when it is at odds with another group.

Independent social groups thus compete with each other for power. Politics among groups is all about gaining relative power. Social groups have a propensity to expand, because greater size usually augments their power relative to rival groups and thus enhances their prospects for survival. Groups can also be bent on expansion for other reasons. They might believe, for example, that they have found the true religion or political ideology, and go on a crusade to export their prized blueprint to other societies. Groups mainly expand by conquering other groups, although occasionally groups with common interests join together voluntarily. Conquerors usually try either to dominate the vanquished group and rob it of its autonomy or else absorb it into its own society. Sometimes they try to wipe out the defeated group. There are limits as to how far any group can expand because the potential victims almost always have powerful incentives to resist and ensure their own survival.

two simple assumptions about human nature: there are significant limits on our ability to reason about first principles, and we are social animals at our core. Taken together, these assumptions tell us three important facts about the world. First, it is populated with a great number of social groups, each with its own distinctive culture. There is no reason to think that situation will change in the near or distant future. In effect, the crucial universal traits of humankind lead us to a world distinguished by its particularism. Second, social groups have no choice but to build political institutions, which means politics and power are at the center of life within societies as well as among them. Third, survival is of overriding importance for individuals as well as social groups. It runs like a red skein through human history.