The European Union enters a new era Saturday when it admits 10 new members, eight of them former communist countries of Central and Eastern Europe. The future is fraught with uncertainty, but one thing is clear: The East and West are coming together, putting their Cold War divisions behind them. A greater Europe is no longer a dream.

Two words seem to define the challenges facing the enlarged EU: unity and diversity. Sacrificing one for the other will not serve the interests of this disparate, sprawling family of 25 nations. The central challenge, therefore, is to pursue these twin objectives in ways that promote peace and prosperity not only in Europe but in the rest of the world as well. Key to this is reducing economic and other disparities within the union, particularly between old (richer) and new (poorer) members.

Peace is the EU's guiding principle. With the ultimate aim of preventing war in Europe, six nations -- Belgium, France, West Germany, Italy, Luxembourg and the Netherlands -- signed the Treaty of Rome and formed the EU under the name of the European Economic Community in 1957.