My guesses : 1: America is a nation of immigrants and the descendants of immigrants. People who emigrate from their home country tend to be more likely to be o

My guesses : 1: America is a nation of immigrants and the descendants of immigrants. People who emigrate from their home country tend to be more likely to be of an optimistic nature (or manic depessive.) 2: Russia's unfortunate history must make for a traumatised psyche in the population as a whole. By contrast America's has been one success after another.