"NATO exists for three reasons - to keep the Russians out, the Americans in and the Germans down." So the first secretary-general of the alliance, Lord Ismay, told a group of British Conservatives in 1949.
Fifty-five years later the Germans are up, the Russians are half in and the Americans half out of the Europe that caused two world wars over the last century.
Yesterday's formal enlargement of NATO to take in Estonia, Latvia, Lithuania, Romania, Bulgaria, Slovakia and Slovenia marks the definitive end of the Cold War for them. The Yalta agreement between Stalin, Roosevelt and Churchill which divided Europe in 1945 has come to an end with yesterday's ceremony. Its passing will be copperfastened by European Union enlargement on May 1st.
Russia opposed this second post Cold War NATO enlargement but could not prevent it. As part of the deal the Russians secured greater consultation and limited participation rights with the alliance, which is no longer projected against it in the same way as it was against the Soviet Union. Most other European and central Asian states, including Ireland, have reached agreements through the NATO-sponsored Partnership for Peace (PfP) to participate in selected NATO activities.
For the Americans NATO remains a crucial political and institutional bridge across the Atlantic. It continues to give them a predominant role by virtue of their overwhelming military superiority. But this is now tempered and balanced by a more equal economic and political relationship with the European Union. It is a difficult adjustment for them to make, even without the growing gulf of values and political approach that has emerged under the Bush administration over the last three years.
There is growing pressure for the US to withdraw troops from Europe or to relocate them within the continent and to project them beyond it to meet the new security challenges from central Asia and the Middle East. This surfaced yesterday in Mr Colin Powell's call for the alliance to become formally involved in Iraq, which was rejected by France and Germany. The debate about the alliance's future role is not yet resolved and will continue. Neutral and non-aligned states such as Ireland have a greater opportunity to participate in it politically through the EU and the PfP.
One recent development that is likely to continue is NATO's involvement in more United Nations peacekeeping and peace-enforcing missions with a formal Security Council mandate. This is in keeping with the UN's increased reliance on regional military forces in Africa and Asia - and the only way NATO could go to Iraq.