The Benefits of a Multipolar World
The world is better ruled by more powers, where old and new powers have balanced influence on world leadership affecting its decisions and planning. They can speak for and support other states inside/outside their alliances, previously marginalized or manipulated by a single/few unopposed superpower(s).
Within international organizations, new superpowers can suggest subjects, dictate terms, block agreements, negotiate with opposing parties, etc. They can even form whole new organizations elsewhere if the old ones are controlled by old superpowers.
The greater world challenges some powers previously couldn't/wouldn't solve alone can better be handled with the new influence of emerging powers: Earth's threats, global equality, international security, gradual disarmament, etc.
A multipolar world limits a single power's transgressions, which gives countries more autonomy, thus better world management—focused, efficient and economical—as with every organization whose members are assigned with different tasks suiting the place each serves: the administrative job of an international body, e.g. the UN, becomes easier when work is divided.
There is less chance for a centralized unipolar world (or even region, that is only regionally harmful), where ONE country is strong and the others are not, as it will always abuse power, like every living organism, caring about its self-interest first and foremost, while encroaching on the interests of other countries that are not powerful enough to object or stop its injustice. Thus it must be "watched & corrected" by proper well-enforced laws. Lawless power is dangerous, and powerless law is useless:
Nations enjoy more independence in a multipolar world:
A decentralized world allows more equality between world regions, limiting migration from marginalized states to centralized ones, as both enjoy similar rights and different privileges. In a power-balanced polycentric world, people won't desert their homeland and flock to a foreign country devoting their physical and intellectual energy to, while causing regression and "brain drain" back home.
They may travel for temporary/personal purposes only, to complete (not replace) each other, to any part on Earth they like without worrying about its "inferiority"—for study, work, trade, culture, or permanent settlement if it best fits one's skills.
The diversity of a multipolar world speeds up the rate of entire human civilization, where aspects of scientific progress (research, inventions, discoveries, etc.) dramatically improve, flourishing and emerging from ALL world regions.
The "gifted" individuals in every country are best benefited from, improving their country, region and world. Human achievements would emerge from all corners of Earth (East, West, North & South: Africa, Latin America, Oceania, etc.), rather than be limited to one hi-tech spot on Earth playing such essential "universal" role, while others merely turn in its orbit. The latter scenario deviates from the natural course of history where achievements were presented by various world civilizations, past and present.
The population of each country can better focus, learn and benefit from their own resources. National issues (politics, social problems, etc.) are better understood and handled by involved insiders, rather than imported, imposed, naturally unsympathetic outsiders with certain expertise "only" needed in specific contexts. Foreigners miss the whole picture of the country they are invited to serve, that only its inhabitants see and live daily. Each country can specialize in the fields it excels at, to complete other countries, rather than adopt/copy foreign patterns or specialties, ignorantly and awkwardly, while ignoring its uniqueness. Its citizens won't import needles or unfit "objects, humans or habits."
Even cultural or linguistic world unity forced by a single power, e.g. Latin in the Roman Empire, or English in the British, then American Empire, used as a lingua franca or cultural common ground, is not only a tragic loss of culture diversity, history and identity, but simply incompetent and politically exploited. A neutral artificial language, e.g. Esperanto or a computerized language, is much more efficient and practical. Otherwise, world countries have every right to neutralize and universalize English, to suit everyone worldwide, as it has become a universal property. The same applies to any Western (Christian European) values carried through western hegemony, compared to the scientifically-tested values of modern social sciences.
The citizens of an economically powerful country/region/alliance have enough self-sufficiency to import "only" what they lack at home. This saves the unnecessary cost of customs, transactions, and shipping, adapting, translating, hosting ... needless foreign elements.
Cooperation between equal world powers better defines the economic role each can play, to create a more diverse world market, without the excess of useless products and shortage of useful others. A multipolar world limits the monopoly of a single power, thus creates a more competitive market over both price and quality. Emerging powers can halt the following:
A multipolar world security is more enduring, because it's based on "mutual interest," not on the false harmony claimed by unipolarists, SUPPRESSING differences, equality and diversity of countries, which inevitably builds up anger and animosity under the surface towards any oppressive superpower trying to keep and define order according to its own terms, only to suit its self-interest.
Internationally, the more world powers, the less chances of power abuse and monopoly by few oppressive countries toward others. Foreign powers find it more difficult to harm an equally powerful state, that is even allied with more states. Nationally, the more powerful and self-sufficient a state becomes, the more internally secure and satisfied its citizens feel, having no urge to destabilize or work against it (e.g. by colluding with home anarchists or foreign intruders).
Some claim a multipolar world may cause problems with world stability if "poles" fight. Untrue, because no powerful country is powerful without being intellectually powerful, thus mature enough to know that fighting other superpowers is depletive and destructive, to its own existence first and foremost, and any short-term self-gains will eventually boomerang, turning into long-lasting losses. Cold wars aren't real wars; they are inactive volcanoes consuming energy and resources inside (e.g. through military/nuclear race) to appease inner fears, until proper laws replace them (e.g. Non-Proliferation Treaty). In fact, every law is an inactive damage "on hold," that anyone can suffer once they break it.
It's ironic that unipolarity advocates claim that the US (the 20th century prominent Superpower) keeps world order by keeping other countries from fighting together, although it's the one that caused more wars and destruction in the world, the only one that used nuclear power for mass killing, and the one most refusing to join any disarmament treaty. Meanwhile, Russia, India, Pakistan ... don't abuse their nuclear powers.
Fear is the best guarantee for safety, whether of law or of another powerful country. The strongest motive why a person/country wouldn't harm another, is fearing the subsequent damaging reaction to one's own actions. Both mutual interests and fears perfectly organize all human relations, provided people "know" what they need and fear first.
Modern humans learned the high cost of war, and the value of diplomacy, communication, and knowledge of others. The least mature country won't choose its own destruction, let alone a wise superpower will. Only a show of power is occasionally needed (as in cold wars), until a world government or better UN is formed, for the security job, rather than "individual" countries taking shifts and forming global vigilance committees as self-assigned policemen.
Being naturally biased, no single country should assume world leadership, but rather many, or even better no country, by having instead a powerful neutral UN fairly representing ALL countries. Before the advancement of 20th century transportation & telecommunication, the UN was impossible, when world powers used to manage their international affairs through long-term diplomacy, as physical and mental communication was limited, making reaching agreements take so long, prolonging and inciting conflicts meanwhile.
Advocates of a unipolar world (typically the jingoists/imperialists from such country or its allies), where one country must be superior to others, claim it's good for world leadership. Such leadership may work in the animal kingdom and primitive societies, not the civilized ones, where an ALPHA MALE has to subdue all tribe members constantly fighting. A strong leadership is needed in the absence of "law & knowledge," which is why an authoritarian regime/superpower benefits most from alienating its subjects/protectorates, breaking the law and manipulating legitimate organizations supervising people's/countries' affairs. It uses its soft power (media, intelligence, diplomacy) to muffle the truth, spread falsehoods, and smother the voices of dissent.
A tribe's head benefits from the ignorance of his tribesmen, about the injustices they suffer, resources they lose, and abilities they possess, which when "focused" much exceed his, him who is a mere mind-gamer, ruling by pretense more than worth (like a lion king whose physical power is easily overpowered by other lions', when united against him, if it only crosses their minds). Knowledge makes people mature enough to enact their own laws governing them, where leaders become mere tools for law enforcement. Gradually, the human tool will be replaced with technology, leaving little for instinctive human bias and power craving.
A center of command has to exist somewhere in world order for better management and effective world decisions. The Center could be a country, many countries, or a neutral body representing all countries. The latter is best for avoiding bias and world centralization that has similar harms to urban centralization's. It's impossible the one at the center can equally reach/help/control those at the ends, as it does those near the center (geographically, but also economically & culturally).