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From the Treaty of Nice to the Treaty of Lisbon

Another Treaty change agreed in Nice in 2001 came into force in 2003. Institutional changes allowed the EU to expand in 2004 to include eight central and eastern European States, Cyprus and Malta.

The institutional structure set up for six States in the 1950s needed further adjustment to cope with enlargement, and following the accession of Bulgaria and Romania in 2007, the EU Treaties were again amended by the Treaty of Lisbon, which came into force in December 2009. This Treaty ended the pillared structure, bringing all but the military aspects of defence into the EU's remit, introducing a President of the European Council, an Area of Freedom, Security and Justice (with an opt-in provision for the UK), and giving a stronger role to national parliaments in the EU decision-making process.

Treaty of Nice

In February 2003 the Treaty of Nice came into force. The main purpose of the Treaty was to facilitate the major EU enlargement (10 new states) which was to follow.

Ten countries joined the EU in 2004: Poland, Hungary, Lithuania, Latvia, Estonia, Slovenia, Slovakia, Czech Republic, Malta and Cyprus. Membership of the EU was 25 countries and 456 million people.

In 2007 Bulgaria and Romania also joined the EU, and Croatia joined in 2013.

Lisbon Treaty

After negative referendums in the Netherlands and France in 2005 on the Treaty Establishing a Constitution for Europe, Member States abandoned this treaty and after a period of reflection, drew up another treaty which was signed in Lisbon on 13 December 2007. The Treaty of Lisbon came into force on 1 December 2009. Lisbon was an attempt to make the EU more democratic, more transparent and more efficient. It led to the appointment of a number of a number of new posts including President of the European Council and High Representative of the Union for Foreign Affairs and Security Policy, which was filled by Baroness Catherine Ashton. The UK Government maintained an opt-in provision regarding the former Justice and Home Affairs matters, in the new Area of Freedom, Security and Justice.

Page last updated February 2014

Brexit: research and analysis


Read research and analysis from Parliament's libraries and committees on how leaving the EU will affect different policy areas in the UK.

Brexit research and analysis