During the first half of the 20th century estimates of civilian and military deaths for the two so called "World Wars" run as high as 100 million. Casualties were very much higher.
During the 40+ years of the Cold War which made up most of the latter part of the 20th century and excluding those regional wars (proxy wars) where the major powers never confronted each other; there is a total estimate of 386 American military personal that lost their lives defending Americans and most of the free world and fewer if any civilian casualties.
The reason was undoubtedly because we developed and maintained the finest combined military force with both offensive and defensive capabilities on land, sea and in the air that the world had ever seen.
While it is likely that many Americans were even aware of what was keeping them safe, it is more than probable that every potential enemy knew that an attack on the U.S. would most likely cause little harm but would bring demolition and devastation of them and where ever they came from.
Domestically the key for our safety was NORAD, the Air Force Air Defense Command and the Army Air Defense which most likely would have taken out any enemy attack by long before they would reach their target.
But couple that with the Strategic Air Command who maintained a very high percentage of their bombers in the air at all times, ready to annihilate any enemy who was insane enough to attack us and you have as we saw a deterrent for any aggression.
While every one who served in each of our armed services in every position contributed to the accomplishment of this world wide mission we especially would like to highlight the Mighty Eighth Air Force and it's members for their continuing tradition of dedication, readiness, skill and performance.