I noticed that Sweden has been successful in pacifying a bitter rivalry with Denmark overtime. Last time they had a conflict was just 200 years ago. But many other countries still have really rancorous rivalries and ethnic conflicts. It seems like once all external threats have been subdued in one way or another, the population has nothing else to do but to improve their own condition, so Sweden blossoming into what it is now makes sense. But how did they do this? Not only integrating leftover Danes from annexing what is now southern Sweden(Scania most notably), they also had an influx of Walloons 500 years ago, Finns 300 years ago, and in the ancient past Geats & Gutes who were conquered. I haven't been successful in finding any books discussing this, only books talking about who conquered what, who went where, who lived where and facts like that.
Why is it that all of these just integrated into Swedish society and accepted their role as Swedes instead of harboring resentment for hundreds of years such as Serbs in Slavonia against Croatia for instance, or Northern- and Southern Yemenites, Catalonians and Spaniards, or ethnicities in Central Asia which have the same predominant religion and history, same ethnic family(Altaic/Turkic), so many centuries of unity through empires, but still they don't count themselves as, for instance, Kazakhs if they are Uzbeks living in Kazakhstan?