On the streets of Najaf, the Spanish soldiers whose withdrawal Prime Minister Jose Luis Zapatero ordered Sunday will scarcely be missed - they account for less than 1 percent of the coalition troops in Iraq.
But among US allies, the new Spanish leader's decision will kindle new flames of doubt, threatening the coalition as governments rethink their commitment in the light of the flaring violence in Iraq and the country's uncertain future. US hopes of persuading NATO to play a role in southern Iraq, for example, appear dimmed.
"If the unrest continues there will be more reservations among countries making symbolic contributions" to coalition forces, "especially if their forces are attacked," says Gary Samore, a Clinton White House adviser now at the International Institute for Strategic Studies in London.
"We know that there are others who are going to have to assess how they see the risk," US national security adviser Condoleezza Rice acknowledged on ABC television Sunday. "I think there are going to be some changes."
Further pullouts would have little military impact, but would send politically damaging messages of distrust about how US forces are dealing with the insurgency in Iraq, and would signal a lack of confidence in the US vision of Iraq's political future, analysts say.
One day after taking office, Mr. Zapatero announced Sunday he would pull Spain's 1,300 troops out of Iraq as soon as possible. He surprised observers by not waiting for a new United Nations resolution, which Washington hopes will give renewed legitimacy to its plans for Iraq.
The quick decision, Spanish political observers pointed out, fulfills a popular campaign pledge and gives him substantial political capital in the run-up to European parliament elections.
"One can deduce that he [Zapatero] arrived at the conclusion, from the contacts he had with [President] Bush or with [US Secretary of State Colin] Powell, that a resolution of the kind he wants is impossible, so it is useless to wait any longer," says Florentino Portero, an analyst at the independent Strategic Studies Group in Madrid.
Zapatero had told parliament he wanted the United Nations to take control of international military forces in Iraq. That would be impossible, given the UN's refusal to engage in "hot wars" or to try to keep the peace where there is no peace.
But demands for an increased role for the UN have been widely voiced by other coalition partners, not least by Washington's most loyal ally, British Prime Minister Tony Blair. "Spain was a specific case, but other countries will look at what happens at the UN and at the prospects for a coherent transition" to a caretaker Iraqi government on July 1, says François Heisbourg, head of the Foundation for Strategic Research in Paris. "Those will be the determining factors."
Special UN envoy Lakhdar Brahimi has won preliminary agreement from Washington and London for his plan to disband the US-installed Iraqi Governing Council on July 1, and to replace it with a caretaker government of technocrats - authorized by the UN - which would prepare for elections next year.
The US would still be in charge of security, however, and Washington's recent behind-the-scenes efforts in Brussels to share the burden by persuading NATO to take command of the central sector of Iraq will probably suffer from Zapatero's move.
"Spain's decision will make it much more difficult to get any agreement, especially given French and German reservations," says Mr. Samore.
The two main foreign pillars of the coalition - the 10,000 British troops, mostly in the southern city of Basra, and the Polish contingent leading a 9,500-man, 23-nation division in central Iraq - appear firm. Other European allies such as Italy have insisted that they will stay the course.
Some smaller countries have also pledged to remain, but they have mostly been careful to keep their troops out of harm's way. Hungary, for example, "has no intention of following Spain's move," says Andras Balogh, chief strategy adviser to Hungary's prime minister. But its 300 men are restricted to transport duty "because the security conditions do not permit more at the moment."
Amid widespread unease about the forceful manner in which US troops are dealing with unrest in Iraq, "those countries involved will increasingly want to make themselves less directly dependent on American operational decisions," says Mr. Heisbourg. "The Spanish were not very happy to find that their forces would continue to run risks in operations decided and led by Americans."
New doubts have arisen in recent days about South Korea's pledge to send 3,600 men to Iraq, which would make it the second biggest foreign troop contributor after Britain. Seoul had already refused to station troops in Mosul, judged too dangerous. The liberal Uri Party, which won last Thursday's parliamentary elections, said the mission should be "approached cautiously," pending developments in Iraq, the Associated Press reported.
It is also uncertain whether the 1,000 or more soldiers from Honduras, El Salvador, and the Dominican Republic, who have been under Spanish command and logistically dependent on the Spanish, would stay after the Spanish withdrawal.
The central question for most countries contributing troops, however, since it will decide Iraq's future, "is whether or not the UN can find members of a caretaker government who are acceptable to key political leaders in Iraq," says Samore.
"It may be too late," he adds, "but if it happens, a new UN Security Council resolution might create the political conditions for NATO to take a greater role."
If the UN fails, however, warns Heisbourg, and "if it seems clear that Iraq is descending into civil war and the United Nations can't do much about it, then you will see folks getting out."
• Lisa Abend and Geoff Pingree in Madrid contributed to this article.