United States has been a sole superpower in the world from at least three decades since the fall of USSR, it dictates in United Nations, declares unilateral sanctions and unilateral war against a sovereign nation, it makes the deal and it breaks the deal with its own terms, and it has maintained its military presence in every continents and ocean. The world is becoming multipolar, the greatest myth, it is a dream for many which unlikely to happen in near future, the United States is a superpower in terms of military, trade, diplomacy, technology, and culture.
After World War II, the western European powers were replaced with two great powers; the United States and USSR, they emerged as a military Superpower in the world, and this ends the global influence of the United Kingdom, France, and Germany. United States displayed smart diplomacy with Western Europe to make them its close allies citing security threat from hawkish communist USSR and smartly formed military alliance with over 28 nations of Europe, Canada in North America, Japan in Asia and Australia in South Pacific, known as NATO, they made non-NATO allies in South Asia, Arabian Peninsula and South America, and most of the allies have been heavily depending on the US for their defense and military technology and so are forced to stay with US terms.
Some of the scholars have been arguing that the world is likely to become a multipolar, Russia, EU, China and India are potential emerging superpower, and they are claiming that Russia in eastern Europe and central Asia, EU in western Europe, China in East Asia and Central Asia, India in South Asia, would influence and would challenge US presence and its interest. It seems the United States is well prepared to take up this challenge, it has almost made them stay engaged with own problem, China is busy in solving its dispute in the South China Sea and economic downturn, Russia is already militarily encircled from all fronts by US allies, it is pushing for the disintegration of the European Union as the mistrust is growing among the member nations, and India has already been engaged with Arch-rival Pakistan in South Asia and has been busy in solving a list of problems, poverty, terrorism, separatism, etc.
There is no country in any corner of the world which can challenge the US influence, EU is the second largest economy in the world but has no military superiority, Russia is military superpower but it is lagging far behind in economy, India and China are more or less on the same page, they have great influence in international trade but have no military and economic might.
The United States is the biggest economy, funds almost every organization in the world, UN, IMF, World Bank, etc, it provides financial aid to almost all the African and Asian countries along with eastern Europe to establish diplomatic superiority, and it has over 150 military bases in the world on the name of international security which they are using to promote their own interest if threatened militarily. Moreover, the US is the technology superpower, almost every important invention, innovation and discovery take place in the United States which ultimately serves the world. Multilateralism limits the American power sphere, it challenges the hegemony of United States, and which would not be acceptable for US lawmakers and Pentagon although it is good for international peace and security.