When the Communities were incorporated into the European Union in 1993, they became its first pillar. The European Coal and Steel Community ceased to exist in 2002 when its founding treaty expired. The European Economic Community was dissolved into the European Union by the Treaty of Lisbon in 2009; with the EU becoming the legal successor to the Community. Euratom remained an entity distinct from the EU, but is governed by the same institutions.
The ECSC was created first. Following its proposal in 1950 in the Schuman Declaration, Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany came together to sign the Treaty of Paris in 1951 which established the Community. The success of this Community led to the desire to create more, but attempts at creating a European Defence Community and a European Political Community failed leading to a return to economic matters. In 1957, the EAEC and EEC were created by the Treaties of Rome. They were to share some of the institutions of the ECSC but have separate executive structures.
The ECSC's aim was to combine the coal and steel industries of its members to create a single market in those resources. It was intended that this would increase prosperity and decrease the risk of these countries going to war through the process of European integration. The EAEC was working on nuclear energy co-operation between the members. The EEC was to create a customs union and general economic co-operation. It later led to the creation of a European single market.
The EEC became the European Community pillar of the EU, with the ECSC and EAEC continuing in a similar subordinate position, existing separately in a legal sense but governed by the institutions of the EU as if they were its own. The ECSC's treaty had a 50-year limit and thus expired in 2002, all its activities are now absorbed into the European Community. The EAEC had no such limit and thus continues to exist. Due to the sensitive nature of nuclear power with the European electorate, the treaty has gone without amendment since its signing and was not even to be changed with the European Constitution intended to repeal all other treaties (the Constitution's replacement, the Treaty of Lisbon, likewise makes no attempt at amendment).
As the EAEC has a low profile, and the profile of the European Community is dwarfed by that of the EU, the term "European Communities" sees little usage. However, when the EU was established the institutions that dealt solely or mainly with the European Community (as opposed to all three pillars) retained their original names, for example the formal name of the European Court of Justice was the "Court of Justice of the European Communities" until 2009