Also, while in the U.S. the so called 'old boys net' helps to get things done, in Latam there's something akin to Chinese guanxi (關係) in getting things done. Relationships are paramount and make corruption endemic and inextricable. It's quite diff from U.S. and euro culture.)))
If I had to pick one thing though, it's the outspoken gregariousness. Europeans are generally pretty reserved; you would never approach someone you didn't know and try to strike up a conversation. A European might tiptoe around a sensitive subject, while people from the USA or South America would be very opinionated and launch into an argument -- even if they don't know you very well.
Also, it doesn't hurt that everyone in South America basically shops at Wal-Mart (seriously, they are freaking everywhere; even more so than in the US).
And not so long ago, corruption was inextricable from business in the US and Europe as well. Trust-busting in the US in the early 1900s broke down the networks here, and WW2 smashed them across Europe, but similar rule-of-law revolutions haven't happened yet in other parts of the world. But they are starting to as the education level rises and the middle-class expands and demands a clean-up.
Well, in honor of the harsh reality USA have also is own quota of this cake, supporting some very shady people in South America in the last decades, like Pinochito for example...
I wouldn't try to link the US' foreign policy to our cultural norms. Foreign policy exists in the realm of realpolitik, and every rational actor would likely behave the same way if they were in the US' place. When it comes to setting the global balance of power, anything and everything is fair game. This is why presidents customarily don't criticize those who come after them.