That's a toughie. Traditionally the US has been 'Top Dog' since the turn of the 20th Century. Involvement in both wars strengthened her position, flexing her industrial might. Then came Korea and the first dent in confidence in the US being able to deliver. Still, they kept up their performance and with UN help (Britain, France chiefly, although Britain could ill afford to send anybody to war so soon after WWII, still less France).
Suez came next. Britain, France and Israel walked into a political quagmire over Nasser and the canal and the US called the shots, ordering us out - or else cough up the war loan, pronto! And then Cuba loomed. Was Kennedy ready to tip the scales with Khruschev? That subsided - sigh of relief. The USSR wasn't ready to plunge into war over Castro.
Vietnam humbled the US though. More in the US were against than for. Crisis time. The Soviets were almost poised to march through Europe, but pragmatism saved the day. Speech-making and muscle-flexing was what it amounted to on both sides. China wasn't ready yet, even though she'd supplied North Vietnam, to take the reins.
Both Bushes pulled us into a police action against Saddam, 'Teflon' Tony was only too ready to oblige there, and we were both dragged into Afghanistan against the Taliban (that the US had armed against the Soviets a decade or so earlier).
Is the US up to another 'police action'? (It's not a war, face it), and who might the 'enemy' be next time? China hasn't been in an external war since the Japanese were drubbed in 1945, and their civil war was hardly epic. Under this regime their financial clout has been going from strength to strength.
Could - or would - the US take on China, should the 'big if' surface? (Don't forget, like the North Koreans, the Chinese are conditioned by blind obedience - how many US citizens these days back the White House right or wrong?)