The role of the US in the world during the past century, although far from unblemished, has been unlike that of any other great power. Not only did it lead the defeat of 20th century totalitarianism, in both its fascist and communist guises, but it allowed the countries in its sphere of influence a unique degree of freedom to pursue their own interests.
However, with the demise of the Soviet Union, the US went from being one of a pair of superpowers to became the sole global "hyper-power". Now, in the absence of a meaningful security threat, the US is unchecked by anything other than its in-built (democratic) self-restraint.
But this has not always been sufficient as the US is presented with an irresistible temptation to go it alone in the world. American unilateralism in recent years has included attempts to impose its domestic laws on foreigners (most contentiously to punish non-American firms for doing business with Cuba and Iran), cruise missile attacks on Afghanistan and Sudan and a refusal to sign up to the International Criminal Court.
Recently, a plan to create a missile shield, primarily to protect the US, has unsettled most non-Americans by threatening to decouple US security from that of Europe and undermine the nuclear deterrents of Russia and China.
The passing of the Soviet threat has also lifted the lid on competing domestic interest groups in the US, who now exercise greater sway over foreign policy. This has contributed not only to increased unilateralism, but also created greater unpredictability. Congressmen, unrestrained by a strong whip system and insatiable in their appetite for election campaign contributions, are easy prey for such interest groups and their lobbyists.
In 1998, protectionists for the first time denied a president "fast-track" negotiating powers - in that case to expand the North American Free Trade Area to include poor Latin American countries. In 1999, isolationists refused to ratify an international treaty to ban nuclear weapons testing.
While US foreign policy becomes less coherent, progress towards co-ordinating the external affairs of 15 EU countries advances at a glacial pace (it will inch forward again at next week's Feira summit in Portugal).
In concrete terms, the advance is often imperceptible.
Even today, their over-riding collective objective - bringing the former communist countries into the EU - is being lost sight of as the narrower concerns of individual member states take precedence. As a result, enlargement seems further away than ever.
Nor have the EU's chaotic institutional arrangements for external relations made progress any easier. Javier Solana, the former NATO secretary-general, occupies the still ill-defined role of the EU's "High Representative" for Foreign Affairs. At the European Commission, responsibility is fragmented, with four departments dealing with various aspects of external relations. To make matters worse, the carve-up of competences between Mr Solana and his Commission colleagues is far from clear cut.
Despite these handicaps, some progress is being made. As an aspiring political union, the development of a defence capability for the EU has moved rapidly up the agenda. In late 1998, France - ever-alert to ways of counterbalancing the influence of the US - persuades a new and unusually pro-European British government of the need for a stronger role for Europe in defence. Since then, the EU has committed itself to the establishment of a "European Security and Defence Identity" (ESDI), including a 60,000 man corps capable of deploying in humanitarian crisis situations beyond its borders.
Sooner or later, these developments will have implications for Ireland. As the other EU neutrals - Austria, Finland and Sweden - reconsider their positions, Ireland may well be faced with a choice to involve itself or accept increased isolation. Debate needs to be encouraged as inaction risks a repetition of the belated but rushed decision to participate in Partnership for Peace - Ireland's first involvement in military co-operation outside the UN.
However, as defence increasingly preoccupies the EU, it has become a matter of contention with the US, exacerbating tensions over trade matters. True to recent form, neither side is entirely coherent in its position.
Although Americans have long pressed Europeans to share more equally the costs of defending their continent, they fret that ESDI will undermine NATO, the main pillar of European security.
But Europeans believe that what Americans really fear is a loss of influence if ESDI succeeds. Moreover, they suspect that the US wants to have its cake and eat it - maintaining its influence over European security through NATO, but have Europeans pay for the privilege.
Financing issues aside, Europeans also say that they cannot be sure the US will always be around to guarantee their security, pointing to the US pursuit of invulnerability with its missile shield as proof of its isolationist impulses.
Americans are on firmer ground when they question the ability and willingness of Europeans to formulate common policies and then back them with meaningful military muscle. They ask whether 15 countries with very different histories and interests can ever hope to agree common positions on security and defence matters - matters that go to the very core of national sovereignty. They also point to ever-shrinking defence budgets in Europe which create a gap between the EU's grand rhetoric and the readiness of member states to pay for expensive military hardware.
But the need for greater balance to the international system will focus European minds on what must be done to co-operated more closely. The only question is how far and how fast it will go. A European counterweight to US global dominance has obvious advantages for all non-Americans. But it is also in Americans' interests.
Our shared constitutional heritage is founded on the need for checks and balances on those who wield power - a recognition that unrestrained power is bad not only for those upon whom it is exercised, but also for those who wield it.
Incoherency on both sides of the Atlantic will make the shift towards a more equal relationship difficult. And with a plethora of issues already causing transatlantic tensions, there is more turbulence ahead in EU-US relations. However, despite a decade of doom-saying, our shared values of democracy, freedom and reason, along with broadly similar interests, have ensured that there has been no return to the shallow peace of 19th century balance of power geopolitics. Despite disagreements about defence and squabbles over trade, fundamental similarities will ensure that the transatlantic partnership endures in the 21st century.
Dan O'Brien is Europe editor at the Economist Intelligence Unit in London.