So apparently you believe that 35 or 40 years is a long time in historical terms.
So if that is the case, then 140 years must be ancient history, and that is when America shed the blood of 500,000 soldiers to end its history of slavery.
If it is truly, as you apparently believe, ancient history, why do you argue so?
America shed its shackles 140 years ago, and the British Empire shed hers 40 years sooner. That makes them relatively concurrent in my perspective, and one shouldn't strut around claiming moral superiorty because their country stopped being evil a bit sooner.