Yes, the US has intervened militarily outside its borders in the past century. But the US is a democratic republic with a market-based industrial political economy. It’s citizens generally lack any self-identification with classical European/Asian imperialism. It’s a nation of business people who want to trade with the world and who fear political impediments to that trade. Despite it’s economic and military predominance after WWI, the US disarmed and withdrew within itself, shunning the League of Nations. Instead of forming a US-led dictatorship after WWII, it led in the creation of the UN. Instead of bombing the Soviet Union during the Berlin Crisis, it organized and sustained an massive airlift of food to Berlin. The list goes on.
So since WWII, the US has had 2 primary focuses: containing communism and keeping markets and resources open to international trade. No American considers the US an “empire” and most resent the suggestion. And, despite America’s assets (listed above) and high patriotism, Americans lack the conqueror’s stomach for blood — his enemy’s or his own. The black civil unrest during the 1960’s would’ve been met with a genocidal response in countries like China