Impressive work. This doesn't come close to applying any sort of consistent standard, of course (I could quibble the hell out of your European map) but still a remarkable effort. And your point is correct, of course, though I suspect we take very different conclusions from it.
Feel free to quibble. I'll probably find a more high-resolution map and do a third version of this, because by the time I got to the Balkans I was so squished in I didn't have the patience for it. Also, some of the boundaries are nebulously defined at best.
21 is pretty dumb, because I) modern-day Italians are not direct descendants of Romans, or at least not any more than they are of Goths, Lombards, Byzantines, Arabs, and others who mixed during the Early Middle Ages while they ripped apart Italy in a zillion of fiefs and II) Italy still for many centuries was a jagged patchwork of Holy Roman Empire dependencies, then city-states, then regional states, the Papal State, dependencies of foreign national kingdoms and what not, and while ordinary people did not necessarily care about this*, most intellectuals were deeply committed to the ideal of a united Italy whereas especially after the XVI century most rulers were representatives of foreign powers (France, Spain, then Austria) which controlled each a piece of Italy and treated it mostly like an opportunity to amass land and power.
*Italian dialects ("vulgar") emerged during roughly the High Middle Ages, so you can trace modern "Italian" ethnicity to then, but what really sparked the flames of national identity in a widespread manner was the French Revolution and Napoleon briefly unifying all of Italy (which was a mess for various reasons and still foreign rule, though).
And this is still an oversimplification!
So, most of Italy was stolen and stolen again and stolen again during the centuries, but unless you are a neo-Bourbonic revisionist reactionary (or an Austrian imperialist reactionary - I'm not sure those exist), the only part that fits the expression "stolen land" is really Südtirol. Or more tenuously, maybe Sardinia, which developed independently from the rest in various ways.
I hope this is helpful!
P.S. Then there is the issue of the incredible amount of groups who lived in pre-Roman Italy, but that was already covered by Antonio.
P.S. P.S. Of course there are similar quibbles to be made with pretty much every European nation, but since Italy has a history of land changing hands a zillion of times during Late Middle Ages and Early Modern era that places like Spain, France and especially the United Kingdom do not have, I think our case is particularly egregious.
