Unipolarity is the centralization and monopolization of geopolitical power, or hegemony, which naturally appears in history as an imperialist and definite being. Though it tends towards centralization ultimately, unipolar hegemons have historically and imperially extended their reaches to the civilizational scale, for both political control as well as plundering the natural resources of foreign soils and sands. Unipolarity is a central concept to the work of Alexander Dugin.
The original unipole of the world came out of a history of tribal and small kingdom warfare, and was called Rome. Rome conquered Europe and gave birth to Britain.
Britain inherited the status of unipolar leader of Western Europe, and helped establish the modern structure of unipolar world order. British colonial imperialism and monarchy gave rise to American pilgrimage and colonialization, through which a sovereign American people eventually turned on British colonialism and British slavery and established independence for itself as the United States of America. America swiftly industrialized and outpaced British colonial and semi-financial imperialism with American financial imperialism (monopolism), and as British unipolarity waned, the US took its reigns. The Suez Crisis in 1956 marked the end of Britain's lead, with President EIsenhower's hard line in Egypt.
After all, both imperialist wars, as Vladimir Lenin points out in his classic pamphlet "Imperialism: The Highest Stage of Capitalism", were fought to consolidate the unipole and decide its leader. Britain was the victor of the first "inter-imperialist" war, and America was the unspoken winner of the second.
American unipolarity is the world order which America uses to lead its "allies" across Europe and their more distant allies across the rest of the world. American President Woodrow Wilson created the League of Nations, which barred the Soviet Union from membership. America holds special powers in the UN, especially in the UN Security Council. The US has the most military bases around the world, owing to its founding NATO as the replacement for Nazi Germany against Russia and Communism. America this has outposts today such as Ukraine and Germany against Russia, Israel and Jordan against Iran, & South Korea, Japan, and Taiwan against China. These three countries represent the main opposition bloc against unipolarity and American imperialism.
After the establishment of a unipolarity, there comes its opposition, its 'other', in the form of malign sovereignty, or the forces of sovereignty and self-determination against unipolarity. Such opposition forces give way to a second pole, creating a dipolarity on the world stage, the first stage of multipolarity, which also appears on a civilizational scale. Thus, America and its allies first combatted the Soviet Union, which cleared all debt including to foreign banks after the revolution, under British leadership; later, after WW2, the United States began the Cold War with the Soviet Union as the first pole, or civilization, to challenge the unipole's hegemony on the world stage. The emergence of a multipolar world beyond its initial dipolar stage would obviously entail more than two poles. Eventually, multiple self-determining and sovereign poles would give rise to a new, multipolar world order, which respects the sovereignty and self-determination of peoples and civilizations.
During Roman unipolarity, such opposition was located in the tribal peoples of the steppes and Africa, as well as the revolutionary early Christians (according to Friedrich Engels). During British imperialism, oppositional forces were located in the colonial resistance and abolitionist movements across Africa, Asia, and the Americas. During American imperialism, opposition was/is located in the Soviet Union (now Russia and China) primarily, anti-war/isolationist movements, labor movements, and Communist or Communist-aligned (socialist) peoples.