Should we apologise for.........?

Should be we continue you apologising for slavery, the crusades, the potatoe famine etc. does it mean anything? If yes, how far should it go? Should the Romans, Vikings, & French apologise for invading Britain; should we ask North African countries to apologise for the white slave trade, would we sleep better at night knowing that the Mongolian government was genuinely sorry for invasion of Europe by Genghis Khan. Should the Russians apologise for the brutal treatment of innocent Germans after the fall of Berlin or the Muslims apologise for 800 years of occupation inflicted on southern Spain. Or how about the Polynesians apologising for the invasion of New Zealand & the genocide inflicted upon the indigenous people there, now annihilated? Why dont southern african countries apologies for the killings perpetrated by their tribal leaders against european men of science who travelled to their lands in the 19th centuary to improve human knowledge of the world? what do you think?