By Kevin Connolly
BBC News, Washington
The centuries of bitterness that divide Christian Armenians and Muslim Turks have spilled onto many battlefields, and it seems strange that they should now be played out in the murmuring corridors and committee rooms of the US House of Representatives.
Accusations of genocide are fiercely disputed by Turks
But there is no doubt that the proceedings of the House Foreign Relations Committee in Washington have become the most important modern theatre of conflict in an ancient dispute.
At issue is a single word - genocide - and the question of whether or not the United States should use it to characterise the deaths of the hundreds of thousands of Armenians who perished as the Ottoman Empire began to implode under the pressures of war in 1915.
To Turks the gravity of the charge is not softened by the passage of the years.
This is a deeply emotional question of national honour, and a charge which threatens to put their nation on the wrong side of history.
To Armenians it is much more that a matter of historical fact - recognition of their suffering represents an important step towards establishing their identity as a nation in the eyes of the world.
To the Obama administration, it is a nightmare - a vivid reminder of how the workings of American congressional democracy can conflict with the realities of wielding power in the White House.
The issue of the Armenian genocide is kept alive in Washington by the tireless efforts of Armenian lobbying organisations.
MASS KILLINGS OF ARMENIANS
Hundreds of thousands of ethnic Armenians killed by Ottoman Turks in 1915-6
Many historians and the Armenian people believe the killings amount to genocide
Turks and some historians deny they were orchestrated
More than 20 countries regard the massacres as genocide
They are usually rated among the most effective in the United States.
Permanent lobbying works in a number of ways.
First and most obvious is the fact that there are congressional districts with substantial Armenian-American populations - representatives from those districts tend to identify strongly with this issue.
Second is the lobbyists' skill at collecting statements of support from candidates in other races.
They have proved remarkably effective at collecting declarations from politicians running for office which tie candidates to the Armenian view of the issue.
That tireless, unglamorous work is an important part of the fabric of American politics - and over time it allows lobbying groups to build strong and lasting coalitions on Capitol Hill.
And that brings us to a major problem for the Obama administration.
Its three most senior figures - President Barack Obama himself, Vice-President Joe Biden and Secretary of State Hilary Clinton - have all publicly identified with the Armenian view of the events of 1915.
That is going to make it more difficult for them to handle Turkish anger over the congressional vote.
When the House Foreign Relations Committee approved the same resolution back in 2007 the Bush administration was able to declare immediately that it considered such statements to be the wrong way of dealing with the issue.
It also worked hard to make sure that the issue did not work its way on to the floor of the full House of Representatives.
The Obama administration can certainly lean on House Speaker Nancy Pelosi to make sure the fallout does not get any worse by ensuring that any further resolutions are quietly placed on the back-burner.
Armenian-Americans are a political force to be reckoned with
Already it is being hinted that the motion will struggle to make it to the floor of the House at a full session.
But the administration will simply have to live the awkward fact that the Turkish government knows that three of the most senior politicians in Washington are simply not on its side.
The secular - but overwhelmingly Muslim - Turkish state has been hugely important to the United States since the early 1950s, when it was developed as a powerful south-eastern bulwark in a Nato alliance assembled to confront the Soviet Union during the Cold War.
It remains important now as a bridge into the Islamic world, as a voice on hugely important regional issues like Afghanistan and Iran - and perhaps above all as a neighbour of Iraq which has been happy to host a strategically crucial US air base on its soil at Incirlik.
Turkey has angrily condemned the congressional vote and recalled its Washington ambassador for consultations - just as it did after the committee vote went against it in 2007.
In theory it has no shortage of options for demonstrating its displeasure with the United States.
In practice however, any reaction is likely to be symbolic and limited. One reason to think so is simple enough.
Turkey has been through precisely this series of events before.
A French parliamentary vote supported the use of the word "genocide" back in the 1990s.
While there was a period of tension and anger afterwards, in diplomatic terms the sky did not fall.
France and Turkey remain important trading partners, just as they were before.
Another is more subtle. One of Turkey's great strategic and economic goals is eventual membership of the European Union, a project in which it has the support of the United States.
At a time when things are not going well in that great project, it would hardly make sense to alienate the United States as well.
So while there is no doubting the depth of Turkish anger on this subject there are reasons to believe that the fallout will not be as dramatic as first reports might have you believe.
While the issue is still immediate and important to both Armenians and Turks, it is rooted in the ethnic tensions and resentments of a vanished empire.
It is hard to imagine modern Turkey risking the wrath of the United States for example by hindering the American withdrawal from Iraq next year as a reprisal.
The safest and cheapest routes for bringing American troops and equipment out of much of Iraq lie through Turkey.
It would be a major decision if the Turkish government escalated this disagreement by making the US evacuation more difficult.
So it is likely that this issue will quickly fade from the headlines again - only to flare once more the next time a parliamentary committee, here or elsewhere, puts it back on the agenda.
The lasting damage will not be in relations between Ankara and Washington, but between Turkey and Armenia.
The process of establishing diplomatic relations was already proving less than smooth and this certainly will not improve it.
The prospects for a joint historical mission to establish some kind of agreed narrative about the events of 1915 now seem uncertain.
The United States and Turkey need each other. Armenia and Turkey are not bound by any such ties of common interest.