1) Black people
2) WW1 and 2.
This.
Black people were seen as "good guys" by the Europeans during the war. We were raised right and a lot of the English, German, French and Italian women were impressed by our swag and respectfulness.
Throw in the Josephine Baker's of the world and people said "ya know, maybe America isn't so bad if they can produce awesome people like this."
Then after WW2, most of the world was on its azz except us and the USSR. So we became the big bad wolf. Been using media, CIA and "diplomacy" ever since. China is the first real challenge to our hegemony in probably 2 or 3 generations but they got so much bullshyt of their own that they can't really challenge us solo.