This post deserves a PSA, because it just went over the heads of 97.8% of USMB posters.
Rome went to hell when Northern Europeans invaded.
Please continue.
Just thinking out loud, it's pretty obvious that America extended, significantly, the English Empire's era of dominance on the world stage. While I would tend to agree that there are differences between the races, culturally and biologically, I've never seen evidence of any superiority of one race over another. The issues regarding superiority of groups usually tend to follow the motives and efficiency, or the lack therein, of their culture. But more particularly, I see the separations as mere happenstance based on the differences for the points in time / initial state of the groups.
For example, our African brothers, just a few generations back were guest workers brought here as slaves. As such it was way to easy for the democrats to buy them with welfare. Eventually they will see welfare for what it is. When they start to see folks like Cosby as their leaders instead of local gang leaders,... well you get my drift.
The only thing constant is change.
While I wouldn't call "our African brothers...guest workers, brough here as slaves, nor would I agree that there are cultural differences between races: Take a white guy, and place him in the Congo for 50 years, and he "goes native." Similarly, take a Vietnamese kid, ship him to the USA, and 50 years later he's the leader of his community and business Tycoon. There are many examples.
The USA is the topic, but your mention of the British Empire is relevant in that the USA, and almost every British Colony succeeded on an unprecedented level above the colonies of every other European nation. This had nothing to do with race (Spaniards and French are White Europeans), but everything to do with culture, and more specifically, law and order. While we may see the USA's revolution against the "superiour" English Law and Order as being a poor example, with the notable exception of a monarchy, the US essentially adopted almost everything in the Consitution from the Magna Carta!
It stands to reason that if governments with the same racial profiles can FAIL on the basis of their consitutions, then governments under different racial profiles can succeed on the basis of their constitutions.