The conflict in Iraq started a century ago. So did the civil war in Syria. And so did Russia’s dismemberment of Ukraine.

All of those conflicts, and much more, grew out of World War I.

At the turn of the 20th century, Europe was prospering. But on June 28, 1914, 19-year-old Serb nationalist Gavrilo Princip assassinated Franz Ferdinand, heir to the Austro-Hungarian Empire, and his wife Sophie.

The following weeks were filled with ultimatums, plans, and pleas. But governments soon found that “control has been lost and the stone has begun to roll,” as German Chancellor Theobald von Bethmann-Hollweg put it.

Among the Great War’s participants, Great Britain enjoyed the best reputation because it was on the winning side and ran the war’s most brilliant public relations operation. Germany’s franchise was in fact broader, though Wilhelmine Germany’s political structure was flawed. Belgium looked to be the most innocent, but its rule killed millions of Africans in the Belgian Congo. France was a revenge-minded democracy. Austro-Hungary was less democratic, but the empire contained important checks and balances within.

A member of the Entente—the allies that included Britain, France, and ultimately the United States—was the antisemitic despotism of the Tsar. Its protégé, Serbia, backed Princip as an act of state terrorism against Austro-Hungary. The sclerotic and authoritarian Ottoman Empire and Bulgaria completed the Quadruple Alliance, while Romania, Italy, and Japan, joined the Entente.

The United States had nothing at stake in this quarrel. Unfortunately, America’s president, the haughty, sanctimonious, and egotistical Woodrow Wilson, imagined himself as being annointed by God to bring peace to the earth.

With Germany facing defeat, an armistice was reached in November 1918. The vainglorious Wilson enunciated high-minded principles for peace, but was out-maneuvered at the Versailles Peace Conference the following year.

The allies plundered the defeated while dictating a vengeful peace. Like the journey from Princip to World War I, the path from Versailles to Adolf Hitler was long but clear.

Wilson’s hope to reorder the world backfired spectacularly. The potentially reforming empires of Austria-Hungary, Germany, and Russia all disappeared. Eastern Europe was filled with what Germans called Saisonstaaten, or “states for a season.” The allies carved up the carcass of the Ottoman Empire, creating artificial entities like Iraq and Syria.

Economic and social crises afflicted even the victors, while the virulent bacilli of communism, fascism, and Nazism were loosed among the losers. The Great Depression spread misery widely.

A generation later, Europeans went to war again, causing more death and destruction. Today, territorial creations in the Balkans and Middle East continue to implode.

Winston Churchill observed in 1936:

America should have minded her own business and stayed out of the World War. If you hadn’t entered the war, the Allies would have made peace with Germany in the spring of 1917. Had we made peace, then there would have been no collapse in Russia followed by Communism, no breakdown in Italy followed by Fascism, and Germany would not have signed the Versailles Treaty, which has enthroned Nazism in Germany.

The so-called Great War demonstrated that appeasement often works. As I point out in my new Forbes online article:

Political figures routinely intone “Munich” without understanding that episode’s unique circumstances. A little more “appeasement” in the summer of 1914 would have prevented World War I—and its many spinoff conflicts.

Alliances often accelerate hostilities rather than deter conflict. In World War I, the two competing blocs became transmission belts of war. Two gunshots in Sarajevo triggered a conflict that eventually reached America.

War is no humanitarian exercise. Countries practiced “war socialism” and sacrificed civil liberties everywhere.

Intervention usually creates additional problems, begetting more intervention. Most every military step, from World War I to the Iraq invasion, spawned new geopolitical crises and demands for military action.

Today Washington is filled with proposals for new interventions. Most seem unlikely to trigger a new world war. But a century ago no one expected a distant assassination to do so either. Americans should make war truly a last resort.