KEY POINTS:
Nothing much will happen right away. The Turkish Ambassador to Washington has gone home for "consultations" after the Foreign Affairs Committee of the House of Representatives approved a bill declaring that the mass killing of Armenians in the Ottoman Empire during World War I was a genocide.
But he will come back to Washington, and it will be weeks before the full House passes the bill. This will be a slow-motion disaster.
The White House tried hard to stop this bill. President George W. Bush declared that "this resolution is not the right response to these historic mass killings". All eight living former US Secretaries of State, Democratic and Republican, signed a joint letter to the Foreign Affairs Committee urging it not to approve the bill.
But it did, by a 27-21 vote, and next month the full House will do the same: more than half the members have signed up as co-sponsors of the bill.
Bush promises that it will die in the Senate but by then the damage will be done. The US-Turkish alliance will be gravely damaged and American use of Turkey as a major supply line for its troops in Iraq - 70 per cent of US air cargo for Iraq goes through Turkey - will be at an end.
"I can assure you that Turkey knows how to play hardball," Egeman Bagis, an adviser to Turkish Prime Minister Recep Tayyib Erdogan, told reporters in Washington. Turkey may also send its troops into northern (Kurdish) Iraq, destabilising the one stable and fairly prosperous part of that country.
The United States will be the 23rd country to fall to the Armenian campaign to link the Ottoman Turkey of 90 years ago with the Nazi Germany of 60 years ago - and, by extension, to implicate the current Republic of Turkey in the crime of premeditated genocide.
Once such a law is passed, to question the Armenian take on what happened is to become the equivalent of a denier of the (Jewish) Holocaust. The Armenian desire to have their national tragedy given the same status as the Jewish Holocaust is understandable but it is mistaken.
The facts are horrifying, and certainly justify calling the events in eastern Turkey in 1915-16 a genocide, but the key elements of prior intent and systematic planning that distinguish the Nazi Holocaust are absent.
When I was a graduate student in Middle Eastern history, as a translation exercise I was given the hand-written diary of a Turkish soldier who was killed during the retreat from Baghdad in 1917. Mehmet Cavus (Sergeant Mehmet) was a youthful school teacher who had been called up in 1914.
At first he had a safe billet guarding the Black Sea entrance to the Bosphorus but in 1915 his unit was suddenly ordered to march east to deal with a Russian invasion and an Armenian rebellion.
And then, in the diary of this pleasant, rather naive young man, I read the phrase "iyi katliam etmistik". Loosely translated, that means: "We really massacred them".
I asked my teacher if it really said what I thought it did. "Oh yes," he said. "Those were different times."
That excuses nothing but it explains much. The foolish young officers who led the Ottoman Empire into the war panicked when they realised that the Russians were invading from the east and the British were about to land somewhere on the Mediterranean coast.
At that point, Armenian revolutionaries (Dashnaks and Hnchaks), who had been plotting with the Russians and the British to carve out an Armenian state from the wreckage of the empire, launched feeble, futile revolts to assist the invaders. The Turks responded by slaughtering many Armenians in what is now eastern Turkey. At least 600,000 died, and perhaps as many as 1.5 million. It was certainly a genocide but it was not premeditated nor was it systematic.
Armenians living in other parts of the empire were largely left alone.
So why is the US Congress "recognising" the Armenian genocide but not the more recent genocide of the Tutsis in Rwanda? Because there are not many voters of Tutsi descent in key Congressional districts.
This is all about domestic politics. Today's Armenian activists aren't looking for "justice". They want to drive the Turks into extreme reactions that will isolate them and derail the domestic changes that are turning that country into a modern, tolerant democracy.
They do not want Turkey to succeed. And Western countries are falling for it.