Why do empires change

Germany
Japan
Spain
England
Holland
Portugal
Italy (home of the great Roman empire)
Greece (home of Alexander the Great)
Scandinavia (home of the original bloodthirsty Vikings)

What do they all have in common?

Once fierce warmongers and conquerors, they've become gentle pussycats. For many of them, the change was abrupt rather than gradual. The Germans and Japanese are the most recent ones. Many of their war victims are still alive today. These countries went from being murderous nationalists to their polar opposite: a rosy picture of tolerance, generosity, patience, and technological excellence.

All have lost the appetite for blood. Germany and Japan once did the unthinkable and they completely turned 180 degrees within one generation.

What happened?

Some say they surrendered because they feared retaliation ala Hiroshima, and for that reason has vowed never to repeat it again. Do you believe that? I don't. Yes it may have been true at the point of surrender but technology turned that around very quickly. As nuclear powers, these countries now have the means to obliterate you with more speed and efficiency than ever before, if they wanted to. In fact with their dwindling natural resources, they now have a bigger reason to strongarm their neighbours and take their assets by force. So why haven't they?

Something must have happened during the throes of war or the period immediately following it. A tremendous shift in mindset which (thankfully) overtook the shift in technology. Something vanished in a people who proved capable of far worse atrocities than we could ever be. What was it?

If we could understand what it was, maybe there is hope yet - for us who have lost all hope in our future.