What about the "historical racism" from, say, Zulu versus Xhosa? Toltec vs. Chichimec? Chichimec vs. what what was to become the Aztec? Aztec vs. just about any other group they managed to conquer (and sacrifice by pulling their hearts out of their living bodies)? Arabs versus Africans of many colours? Arabs versus whites? The slavers of the Barbary coast - that is, (Islamic) pirates who operated from the coasts of northern Africa - captured and sold millions of light-skinned Europeans on the slave markets in what now is Libya, Algeria, Tunisia and Morocco, why aren't they up in arms against this "historic racism"?. It took the French conquest of the area to finally put a stop to those slave raids - maybe the French were justified in conquering a region from where pirates had been raiding French (and Italian and Dutch and British and even Scandinavian) villages from where they took slaves to the markets of Tripoli? The Ottoman empire was rife with slave trade but not much is made of that for some reason, why? What happened to the Picts who inhabited the British islands? The Irish and Italians were subject to racism and enslavement but I have yet to see any of them call for retributions, why is this?
Do you know the etymology of the word "slave", that is comes from the Slavic tribes who inhabited central Europe and were enslaved by Arabs: 'The Slav was the most prized of human goods. With increased strength outside his marshy land of origin, hardened to the utmost against all privation, industrious, content with little, good-humoured, and cheerful, he filled the slave markets of Europe, Asia, and Africa. It must be remembered that for every Slavonic slave who reached his destination, at least ten succumbed to inhuman treatment during transport and to the heat of the climate. Indeed Ibrāhīm (tenth century), himself in all probability a slave dealer, says: "And the Slavs cannot travel to Lombardy on account of the heat which is fatal to them." Hence their high price.' (The Cambridge Medieval History, Vol. II, 1913).
I can go on forever for the history of humanity is indeed a sordid affair, riddled with accounts of cruelty and - seen through modern western eyes steeped in Judeo-Christian morality - truly proof of the fallen nature of the human race. I won't since it doesn't change the fact that societies and cultures rise and fall through conquest, then and now. Claiming, as you do, that "...the reason their country is a horrible place to live is because of historical racism in the form of colonisation on the part of European countries or the USA" is myopic, it stems from a vision of the world as a European/American-centric place where all roads lead to Europe and America.
This self-flagellation which is so popular in many western cultures needs to stop or those same cultures will succumb to the process of history which gave rise to them in that other cultures will take over. Many of those cultures don't care about racism - they are openly racist - and have no qualms about slavery.