European integration began with the Treaty of Paris in 1952 which established the European Coal and Steel Community. This established a common market for coal and steel for Belgium, France, Germany, Italy, Luxembourg and the Netherlands. It was a move partly motivated by the need to create common economic interests within Europe, in the hope that this would avoid the continent descending into war for a third time.
There arose a political impetus towards further integration, leading to the Treaties establishing the European Economic Community (EEC) and the European Atomic Energy Community (Euratom) in 1958. The concept of a common market was at the heart of the EEC treaty, encompassing the abolition of customs duties between Member States and the free movement of goods, services, people and capital within the EEC. This led to agreement on a number of economic policies for the EEC, including the Common Agricultural Policy and the Common Transport Policy.
The UK joined the EEC in 1973. Since then the treaties underlying the union have been substantially amended, and membership of the EU has been expanding. The Single European Act in 1986 led to greater steps being taken towards ‘completing the internal market’ (i.e. achieving greater economic and competitive integration between Member States) and brought new areas (such as social policy and environmental protection) with the remit of the European Communities.
More changes came with the Maastricht Treaty in 1991, including the new name European Union, a new legal and political framework and the introduction of a number of new policy fields. The previous treaties were replaced by the Treaty on European Union which, amongst other things, provided for European action in the fields of foreign and security policy and justice and home affairs (policing). It also provided for a move towards European monetary union, the establishment of the European Central Bank and the creation of the Euro as a single European currency. The UK ratified the Maastricht treaty, but opted out of the provisions on European monetary union and common social policy.
There have been several further rounds of treaty amendments since the Maastricht Treaty. The changes have included changes to the EU’s institutional structure and processes and the addition of new policy areas. Notably, there has been considerable enlargement of the European Union, by the accession of a number of new Member States. The latest major amendment to the constitutional basis of the EU, the Treaty of Lisbon, came into force in 2009.
There are currently two principal treaties (as amended by the Treaty of Lisbon): the Treaty on European Union (originally signed in Maastricht in 1992) and the Treaty on the Functioning of the European Union (originally signed in 1958 as the Treaty Establishing the EEC).