LONDON -- The symbolism could hardly have been better. Against a background of the columns of ancient Athens, the birthplace of democracy, 25 government leaders signed documents that will bring into the European Union countries that spent much of their postwar existence under communist dictatorship.

Although the air was full of talk of a breakthrough, the enlargement, which takes effect in May 2004, will come as the 15-nation union faces some of the toughest questions of its history.

The biggest immediate problem arises from the division over the war in Iraq between Britain, Spain and other EU members that backed America, and the antiwar party led by France and Germany.