By Chris Morris BBC Europe correspondent in Copenhagen

All's well that ends well, they say, but this process is not over.

The European Union is right to pause for a moment of celebration as it ends its landmark summit in Copenhagen, but there is plenty of hard work ahead.

For months leading up to this summit, negotiations have been truly tough; on enlargement, on Turkey and on Cyprus.

It is hardly surprising, because the future political map of Europe has been drawn here.

In the crowded halls of a Copenhagen convention centre, it is hard to sense history in the making.

But inviting 10 new countries to join the EU, most of them from the former communist bloc, is a huge decision.

It will take years for the newcomers to be fully integrated, years for the economic benefits to materialise

It is a decisive moment in the development of the union - from now on, said the UK Prime Minister Tony Blair, it will be a fundamentally different Europe.

But the enlargement deal has to be ratified next year - by parliaments in the existing member states, and by the people in all but one of the candidate countries.

There are sceptics at every turn, who wonder what is in it for them, and how EU institutions will function efficiently with 25 member states.

The new enlarged Europe will be the biggest single market in the world, with more than 450 million people.

The Turkey question

And there will be more to come. Romania and Bulgaria are on schedule to join in 2007, and Turkey may finally begin negotiations on membership in two years time.

It will take years for the newcomers to be fully integrated, years for the economic benefits promised by the EU to materialise. But it is a turning-point, even if there are still real problems to overcome.

Can the EU really assimilate a large Muslim country?

One of the 10 candidates, Cyprus, may enter the EU as a divided country. Negotiations on re-unifying the Greek and Turkish Cypriot sectors will continue.

But there is no guarantee of success, and that could mean that in two years' time, Turkish troops in the north of the island will be occupying EU territory.

The new reformist Turkish Government says it wants to reach a deal on Cyprus. But what about the Turkish army?

The generals see their military presence on the island as a vital strategic asset - they will not give it up lightly.

And then, of course, there is the issue of Turkey's own membership bid.

Across Iron Curtain

Since the days of the Ottoman Empire, Europe has agonised about its eastern question - what to do about Turkey. And nothing has really changed.

Can the EU really assimilate a large Muslim country?

The British Government, joined by several others including Greece, says yes it can.

But some countries have their doubts, and they will continue to argue for caution.

As the EU expands to the east, across the old Iron Curtain, the debate about how and where Europe defines its outer limits has not yet been resolved.