The creation of a customs union in the European Economic Community in 1968 was implemented internally through the abolition of customs duties, quantitative restrictions and measures having equivalent effect between Member States [see section 5.1.1] and, on the external front, through the introduction of a common customs tariff and a common commercial policy. In fact, goods imported from third countries had to be treated in the same way by all Member States in order to circulate freely in the customs union [see section 5.2]. But the customs union itself had to be integrated into the existing international economic order, regulated by the 1948 General Agreement on Tariffs and Trade (GATT).
This is why, in Article 110 of the EEC Treaty [Article 206 TFEU], the Member States declared that in creating a customs union, they intended to contribute, in accordance with the common interest, to the harmonious development of world trade, the gradual removal of restrictions to international trade and the lowering of customs barriers. They have kept their word. The creation of the customs union has led to strong growth in intra-Community trade, but the Community has not become introverted. Instead, it has developed into the world's biggest importer and exporter. In addition, the rules of the GATT [see section 23.4], and the various international agreements drawn up under its aegis, formed the legal basis for the EC/EU's own commercial policy instruments and action, notably in the field of tariffs, the application of safeguard measures, anti-dumping and anti-subsidies actions.
In accordance with Article 3 (1)(e) of the TFEU, the European Union has exclusive competence with respect to the common commercial policy. Accordingly, only the Union may legislate and adopt legally binding acts within that area. The Member States are able to do so themselves only if so empowered by the Union, in accordance with Article 2(1) TFEU.