Those who remember the end of WWII  will remember the  popular theme of "The End of Nationalism."  With tens of millions dead and much of Europe and Asia in ruins, the world turned to new forms to end old conflicts.  We understood what resulted when citizens got fired up in their ancient tribal emotions and chose arrogant, xenophobic leaders.  

Other than the Cold War, what followed was an era of brotherhood and cooperation, especially in a Europe which vowed "Never again" to war.  Traveling across Europe and staying in campgrounds in the summer of '72 we saw nothing but good feelings and  cooperation among international travelers.  
Structurally, this friendship was institutionalized by the UN, EU, etc.  Now we're in a risky new era, marked by  the weakening of old structures, rising nationalism and aggressive new leaders such as Trump, Putin, B. Johnson,  Le Pen, Wilders,  etc.  As nations resume their old habits of pushing out against others, the future is a bit scary.