Does "you shall not detest an Egyptian, because you were an alien in his land" extend to not hating Spaniards, Germans, and other former oppressors?
Note that the Torah only explicitly refers to the (men) of Amon and Moav as well as the nation of Amalek because of what they explicitly did to deny hakaras Hatov. The gemara says that the descendants of Haman taught Torah in Bnei Brak. The discussion involves whether we are allowed to accept a convert even from Amalek to show that they can do Teshuvah. Even the Mitzriim are to be remembered for the fact that once they purge the evil that is in them (after three generations of having converted) are to be accepted as full Jews. Every other nation (except Amon and Moav) are to be accepted at once. Nevuzaraden the butcher was accepted after he did teshuvah. Shmaya and Avtalyon were descendants of Sancheruv.
We see that we must accept anyone who does teshuvah unless specifically commanded otherwise in the Torah. Thus, we should accept that the Spaniards, the Germans, and other nations can do teshuvah and truly repent of the evil that their ancesters did. However, this also means that if people insist on being reshayim, then we cannot forgive them. A person who insists on doing evil, is to be "hated". Not because of any intrinsic characxteristic, but because of the evil that he does and the fact that he makes himself an enemy of Hashem.
When the Egyptians drowned in the Yam Suf, Hashem stopped the malachim from singing praise because the Egyptions were also His creatures. However, He accepted the song of praise from the Bnei Yisrael, because that was proper for them to do.