In April 1923 the last U.S. troops pulled out of Germany. They had been there since the Armistice of November 1918, to help stabilize the country’s fledgling democracy after Germany’s defeat in World War One. American commander General John Pershing was opposed to the withdrawal. He warned the politicians that if we left, we’d have to deal with Germany again in twenty years.

But after losing 126,000 Americans in the war to end all wars, the American public was sick of foreign entanglements. Let Europe and the rest of the world take care of itself, people said; we want our boys home.

So last troops did come home, and in less than two decades Pershing was proved right. The Americans who returned at Anzio, Cassino, and Omaha Beach paid in blood for their countrymen’s desire to not to be bothered with a war’s aftermath.

Now we’ve see the last American troops leave Iraq. No sane person can begrudge the families of those who have served, and those who died, for welcoming the end of the mission–and it would be foolish to predict what Iraq will look like in 2031, let alone if American soldiers and Marines will have to die there again.

Still, it’s clear the United States has surrendered any leverage over what does happen in Iraq. and yesterday's bomb blasts in Baghdad killing 57 and wounding at least 200, are a chilling foretaste of what might be coming. Instead, we’ve left the one Arab democracy in the region–one we sacrificed 4,500 American lives to establish–to deal with its problems and its neighbors alone.

One of those neighbors is Iran. The mullahs in Tehran will see the American pullout as leaving a power vacuum they will be anxious to fill. Even if Iraq’s Shia majority doesn’t want to bow down to their fellow Shias in Iran, Iran will be free to play its hand in shaping Iraq’s future–especially through its proxy Muqtada al Sadr and his militias. That’s not a future anyone in Washington is going to like.

Then there’s Syria. Its dictator Hafez Assad kept the Sunni anti-American insurgency supplied with arms and warriors all through the Iraq war. He will want to play the role of protector of Iraq’s Sunni minority in its aftermath. Even if Assad doesn’t survive the rising tide of the Arab spring, any future government in Syria will see playing Sunni versus Shia as key to its Iraq policy–even if it means instability in Iraq itself.

Finally, there’s Turkey. They’ve been having an ongoing war with Iraq’s Kurds–the one group who’ve been pro-American from the moment Saddam Hussein fell from power in 2003. Now that the Kurds’ American protectors are gone, they will feel increased pressure from Turkey-as will the government in Baghdad. Like Syria, the Turks see American withdrawal as our loss and their gain, in influence–and like Syria, they already see Iran as the power to court, not America.

In short, we’ve left Iraq in a bottle with three scorpions–with no help from us except kind words.

How that fledgling democracy, made up of three ethnic and religious groups who until recently were murdering each other, will deal with the scorpion bottle is anybody’s guess. T

here’s also a lot at stake, with Iraqis sitting on the third largest oil reserves in the world–close to 145 million barrels. Iraqis have sacrificed their liberty for national survival before, under Saddam Hussein. They may have to do it again.

But one thing is clear. If we don’t like the outcome, we will have no one to blame but ourselves.

Arthur Herman is a historian and author of the Pulitzer Prize finalist "Gandhi and Churchill: The Epic Rivalry That Destroyed an Empire and Forged Our Age (Bantam, 2008)," His other books include the Mountbatten Prize–nominated "To Rule the Waves: How the British Navy Shaped the Modern World (HarperCollins, 2005)," the New York Times bestseller "How the Scots Invented the Modern World (Three Rivers Press, 2001)," and many articles on foreign and military policy. He is a visiting scholar at the American Enterprise Institute