Late last month, Britain, France and Germany rose in unison, flexed their muscles, and rammed a vote through the International Atomic Energy Agency condemning Iran for its nuclear transgressions. This forceful action by the "Euro 3" was a distinct surprise-given the fact that two of the three, France and Germany, had opposed taking strong measures against Saddam Hussein in 2003, when his willingness to disarm was being questioned.

The explanation for this new behavior is that Saddam has taught the West a lesson: to stop the spread of the bomb, Europe and the United States must stick together.

The European response to Iran's nuclear transgressions has been unyielding. In an op-ed in the Wall Street Journal on September 22, the foreign ministers of the three European powers, along with EU foreign policy chief Javier Solana, argued that under IAEA rules Iran should have been sent for punishment to the U.N. Security Council two years ago, when its nuclear violations were first revealed. The ministers warned that "the proliferation risks if Iran continues down its present path are very great," and they showed they were willing to resort to punitive action-even in the face of strong opposition-to mitigate those risks.

Before forcing the vote at the international agency, the Euro 3 had taken the lead in negotiating with Iran to give up its sensitive nuclear work. They brokered two deals that froze uranium enrichment and plutonium reprocessing-activities that could provide Iran with the means to make fuel for nuclear weapons-and forced Iran to provide the IAEA with information on past nuclear work. The negotiations broke down in August, when Iran resumed uranium work at its plant in Isfahan and rejected a European proposal for long-term cooperation in a number of areas-including nuclear energy.

The United States too has learned a lesson from Iraq: going it alone has costs. The 2003 U.S.-led invasion did not secure or protect Iraqi weapon sites. Instead, it sunk U.S. credibility around the world. The United States learned that a unilateral invasion was not an effective arms control strategy.

In light of this experience, the United States has been more cautious in dealing with Iran. The Bush administration explicitly endorsed Europe's diplomatic initiative in March 2005 and has toned down rhetoric demanding that Iran be sent without delay to the U.N. Security Council. Instead, the United States now appears willing to wait for Europe's effort to run its course. On September 14, U.S. Secretary of State Condoleezza Rice admitted as much, saying that Security Council referral "is something that we'll be working for a while," but that the United States is "not so concerned about exactly when it happens."

What Russia and China, both of whom abstained in the recent IAEA vote, may have learned from Iraq is less clear. Both supported Europe's negotiating effort, but neither is prepared to tighten the screws now that those negotiations have failed. Their strategic and commercial interests-formerly with Iraq, now Iran-still seem to rule their every action.

The new unity between Europe and the United States suggests that neither wants to relive the years of acrimonious debate that spoiled their approach to Iraq. The battle created a rift in transatlantic relations and a divide among European powers. France and Germany were left criticizing the United States from the sidelines, and Britain wound up an unequal partner in the U.S.-led military coalition.

The Iranian nuclear crisis is the first test of how much the West has learned from its mistakes. It will need to remember the lesson well in the months ahead-which are sure to grow ever more contentious.