The citizens of the United Kingdom have voted to leave the European Union.
In doing so, they have undone a half-millennium of work toward pacifying the most war-torn continent on the planet earth.
Europe has always been at war with itself. The Pax Romana never fully pacified the Germanic tribes. Strife was frequent through the Middle Ages. The battle of Agincourt solidified enmity between the English and the French.
The Thirty Years War was one of the bloodiest conflicts in the history of mankind. The Napoleonic Wars shook the world. And the world wars of the 20th century killed about half as many people as had existed on the entire planet at the time Julius Caesar conquered Britain for Rome 2,000 years earlier.
After many of these wars, there were attempts to achieve peace among the war-torn nations of Europe. The Peace of Westphalia, the Congress of Vienna, and the Treaty of Versailles all aimed to create a peaceful European system.