By William Horsley
Writer on European affairs
The European Union claims it has secured peace among historical enemies, spread democracy to its neighbours and created a new model of international co-operation.
But none of that was pre-ordained.
The milestones of the past 50 years tell a story of bitter national rivalries, personality clashes and tortured compromises which have threatened the project's survival more than once and may do so again in the coming years.
Winston Churchill, Britain's wartime leader, called postwar Europe "a rubble heap, a charnel-house, a breeding-ground for pestilence and hate".
Churchill saw European unity as a means of breaking the cycle of conflict
The challenges for Europe included the retreat from colonial empires and the imminent security threat posed by the Soviet Union's domination of eastern Europe.
But a different concern motivated the architects of the European integration project - fear of an over-mighty Germany.
The story began as a search for an over-arching political framework to tie West Germany's destiny to that of its western neighbours and make another war impossible.
The first attempt ended in fiasco. In 1952 six nations signed an ambitious treaty to set up a European Defence Community as a rival to the US-led Nato alliance.
But the French parliament rejected the plan, judging that it would be too weak to allow France to keep the upper hand over a revived West Germany.
Economic integration proved more fruitful. The European Coal and Steel Community had shown the way by pooling national sovereignty in key industries.
De Gaulle triggered the "empty chair" crisis
The Treaty of Rome built on that to unite France and West Germany, together with the four other founder members, in a European Economic Community.
But the fledgling EEC soon faced another life-threatening crisis.
In 1965, an imperious French President, Charles de Gaulle, threatened to wreck the EEC unless the others acknowledged France's special role in taking the Community's big decisions, especially over the Common Agricultural Policy's system of lavish subsidies, of which the lion's share went to French farmers.
The result was the "empty chair crisis", a French boycott of EEC meetings which forced the rest to agree that each country would keep the power to veto common decisions to protect its vital national interests.
Thus France firmly staked its claim to ownership of the European project.
And Charles de Gaulle acknowledged his motives in vetoing the UK's attempts to join the EEC until 1973. Britain, he feared, would be a "Trojan Horse" for American influence.
That mistrust pointed to what was to come - a titanic, ongoing struggle among European states between a French-inspired Euro-centric, dirigiste vision of the Community's purpose and a looser, free-market and Atlanticist vision championed by Britain.
With the fall of the Berlin Wall in 1989 and the end of the Cold War the political battle for Europe was joined again with renewed fervour. European leaders ruled that German re-unification must be accompanied by a new effort to unify Europe politically.
Yes and No: Mitterrand the motor, and Thatcher the reluctant European
Two formidable figures, Chancellor Helmut Kohl of Germany and President Francois Mitterrand of France, forged a uniquely close alliance and claimed a special role as the joint "engines" of European integration.
They made history by paving the way for the euro currency and the Maastricht Treaty which was to establish a European "Union".
But to latecomers such as Britain and Denmark it was all very hard to swallow. A breaking-point seemed close when in 1990 Britain's Prime Minister Margaret Thatcher stridently rejected the prospect of more powers being signed over to European institutions, saying: "No.No.No."
That immediate crisis passed when Mrs Thatcher was ousted from power at home.
But the underlying tensions remained. The idea of a "two-speed" Europe took root. Some nations embraced more common policies, such as the currency union, while others stood aside.
End of a dream
And the EU faced another Catch 22: the "widening" of the Union through enlargement clashed with its long-standing commitment to "deepening".
So by the year 2000, as the EU prepared to mark its triumph in bringing Poland and other ex-communist states into the European family, Europe was in other ways already coming apart.
In 2003, the Iraq war again exposed an old fault-line between Atlanticists and the Franco-German camp, this time allied with Russia too.
TREATY OF ROME
Signed 25 March 1957 at the Palazzo dei Conservatori, Rome
Original name: Treaty establishing the European Economic Community
Key objectives: a common market and customs union; ever closer union among the peoples of Europe; pooling of resources to strengthen peace
Signatories: Belgium, France, West Germany, Italy, Luxembourg, the Netherlands
Came into force on 1 January 1958
So the 2005 crisis over the draft European constitution brought together an explosive mixture of disputes and resentments, over the EU's power structures, its foreign policy orientation and social policies, in one moment of decision.
Not surprisingly, something snapped - the patience of French and Dutch voters, who said No.
The Prime Minister of Luxembourg, Jean-Claude Juncker, lamented that the people of Europe had stopped believing in the "European dream".
Yet the EU goes on into its second half-century.
The pioneers of the European project talked much about the finalite politique - the political destination.
They were wise enough, though, not to define it. Because obviously, nobody knows.