May 1, 2004 cartoon by Chapatte celebrating European enlargement
In 2001, the Treaty of Nice was signed. It was intended to improve the Maastricht Treaty and bring greater democracy to the European institutions in anticipation of further enlargement: one Commissioner from each member state; the weighting of votes in the Council (i.e. the bigger the country in terms of population, the more votes it has at the European Council).
The Euro became the new currency for eurozone countries in 2002.
During 2003, the member states did not act in a concerted manner regarding the Iraq War, showing up the lack of influence of the EU in international relations (basically, each country continued to act on its own).
2008 cartoon by KS
In 2005, the project for a Constitution, elaborated by a team headed by Valérie Giscard d’Estaing, was rejected by the French and Dutch in referendums, putting a brake on political integration. However, enlargement went ahead in the same year: ten east-European countries from the former Soviet bloc joined the EU. This added 75 million new citizens. Their integration was not easy as their standard of living was very low, though some countries, such as Poland, have made spectacular progress. In 2007, Romania and Bulgaria also joined.
The Great Recession which started in 2008 undermined the efficacy of the Euro.
The 2009 Lisbon Treaty was intended to modernize EU institutions to better cope with enlargement.