During this period the USA has been involved to a greater or lesser extent in various regional wars (probably most famously, the Vietnam War), and has maintained espionage and covert operations in many other areas.
The term "Pax Americana" is used by critics of American policy to describe a supposed effort to suppress countries which do not cooperate with American policy (so called rogue states). This usage by critics seems meant to imply that the Roman Empire was immoral in some way or is perhaps sarcasm. Also, some supporters of American foreign policy also use the term, so it is not necessarily a derogatory term.
Many supporters of the USA do not consider the country to be imperialist, and argue that it has a long history of isolationism - which subsided only after major shocks in 1900, 1917, and 1941 (and, some would argue, in 2001). Many people believe that the United States has sought, or has found itself forced into, a quasi-imperialist role by its status as the world's sole superpower. However, the term "isolationist" in this context applies to the global stage; the United States has never been isolationist with respect to the Western Hemisphere, which it has considered to fall within its sphere of influence, and has a long history of military intervention within this region of the world, in the spirit of the Monroe and Truman Doctrines.
The fiercest debates between isolationist and imperialist factions were probably at the end of the 19th century, when those who favored U.S. control of Hawaii and the Philippines, the "jingoes", including Theodore Roosevelt, debated hotly those who favored traditional American policies of avoiding foreign entanglements, including Samuel Gompers, Andrew Carnegie, and others (who came from a very wide variety of backgrounds and were opposed on almost every other issue). At that time, the term "imperial" was indeed used as a positive goal by jingoes and as a negative term by opponents. When Theodore Roosevelt ascended to the Presidency on the assassination of William McKinley, in 1900, US foreign policy began to undergo its first major shift away from isolationism towards a policy of foreign intervention.
Generally, supporters of US foreign policy regard interventions by the USA as forced upon it by moral necessity or self-defense (including defense of US national interests abroad, which are often interpreted by critics as purely economic interests such as access to petroleum reserves). Criticism of American foreign policy is sometimes labelled as Anti-Americanism by those on the right, although the precise meaning of this term is nebulous. Supporters of American foreign policy tend to describe world affairs in moral terms, rather than in terms of realpolitik or moral equivalence. This can create a perception that the US right believes the US is morally infallible, which causes some critics to view the United States as arrogant and disrespectful of the rule of international law. A common counterargument is that many of the institutions of international law (e.g. the United Nations) have no real moral or political authority, since a significant number of their member nations are not democracies and/or have a poor human rights record.
See also: History of United States Imperialism, Cold War, American Empire, British Empire, white man's burden, Monroe Doctrine, Truman Doctrine, Bush Doctrine, Project for the New American Century, hegemony