In 1921 Luxembourg, a former member of the Zollverein, signed the Convention of Brussels with Belgium, creating the Belgium–Luxembourg Economic Union. Belgium and Luxembourg thereby had the same customs tariff and a single balance of payments since 1921.

The union was expanded after World War II to include the Netherlands. At the beginning of 1948 most import duties within the Benelux area were abolished, and a common external tariff was put into operation. Exceptions were made, nevertheless, for a few agricultural products, and it was also felt necessary to introduce a system of quotas.

It was rapidly perceived that a simple customs union was inadequate, and a treaty on October 15, 1949, set as its target the progressive and complete liberalization of trade between the partners, systematic coordination of their international commercial and monetary policies, and the adoption of a joint bargaining position in negotiations with other countries. Though the experiment was optimistically viewed everywhere as the precursor of a wider European economic integration, it faced difficulties arising from the very different postwar situations of Belgium and the Netherlands. The two economies were competitive rather than complementary. Other problems arose in connection with the free access of Dutch agricultural products to the Belgian market. Moreover, the Belgian economic system was more liberal than the Dutch, where rigorous price control had long been a standard practice.

The development of Benelux received strong impetus from the formation of the European Economic Community in the 1950s. When the Treaty of Rome in 1957 created the EEC, or Common Market, it spurred the members of Benelux to confirm and strengthen their own integration in the Benelux Treaty of Economic Union signed at The Hague on February 3, 1958. The Hague treaty, however, contained little that was new, and in outline form it was no more than the codification of results already achieved.

The Benelux Economic Union made all of its decisions unanimously, and all members of the union became founding members of the EU.

An important step in European integration was taken in May 1950 when the French foreign minister, Robert Schuman, proposed that a common market for coal and steel be set up by countries willing to delegate powers over these sectors of their economies to an independent authority. The motive behind the plan was the belief that a new economic and political framework was needed if European unity was to be achieved and if the threat of a future Franco-German conflict was to be avoided. In April 1951 France, West Germany, Italy, and the three Benelux countries signed a treaty in Paris setting up the European Coal and Steel Community (ECSC).

The signatories bound themselves to abolish all customs barriers and other restrictions on the movement of coal and steel between their countries; to renounce all discriminatory practices among producers, purchasers, or users (with respect to price and delivery conditions, transport charges, selection of suppliers, etc.); to end government subsidies or grants-in-aid; and to eliminate all practices interfering with the operation of markets.

When first promulgated, the constitution of the Coal and Steel Community allowed that it be governed by a High Authority, assisted by a Consultative Committee, a Common Assembly, a Special Council of Ministers, and a Court of Justice.

There was, however, a basic incompatibility between the community’s provenance, limited to the coal and steel industries, and the sovereignty of the member countries, each of which was responsible for its own general economic policy. As a practical matter, during the first 17 years of the community’s existence, authority on all substantive issues remained vested in the national governments. The High Authority was autonomous only in matters of secondary importance. Thus, the coal crisis of 1958—when West German, Belgian, and French stocks of unsold coal rose to unmanageable proportions—was resolved at the national level. All the High Authority could do was to confirm the measures taken, even when they were contrary to the provision of the treaty. Similarly, the reduction of the labour force in coal mining from 650,000 persons at the end of 1957 to 300,000 10 years later was effected by individual countries; there was no communitywide action.

The treaty reserved for member countries responsibility for their own trade policies toward third countries. This hindered the establishment of an effective common market since a common market requires a unified system of protection from foreign competition. At the height of the coal crisis, for example, when stocks of coal rose in Belgium, West Germany, and France, Italy nonetheless continued to buy cheap supplies from the United States.

Despite such difficulties much was accomplished by the community. The markets for steel and coal were liberalized to a considerable degree; the community served as a useful forum in which questions of common interest could be examined; and it fostered the growth of an international spirit, which did much to facilitate the negotiation of the Treaty of Rome and the creation of the EEC and the European Atomic Energy Community (Euratom). These advances contributed to the formation of the EU.

The European Coal and Steel Community represented only an initial step in the movement for European integration. On March 25, 1957, its six member governments signed the Treaty of Rome, under which they agreed to establish the European Economic Community, or Common Market, which came into being on January 18, 1958. It expanded with the entry of the United Kingdom, Ireland, and Denmark in 1973, Greece in 1981, Spain and Portugal in 1986, and the former East Germany as part of reunified Germany in 1990. In the process, it represented the most far-reaching attempt at economic integration among sovereign countries. Its founding treaty stands as the model, in whole or part, for all subsequent attempts at economic integration.

The Treaty of Rome aimed to “establish a common market” and “progressively bring the economic policies of members into alignment” so as to

promote the harmonious growth of economic activity in the Community as a whole, regular and balanced expansion, augmented stability, a more rapidly rising standard of living, and closer relations between the participating states.

The treaty pledged the signatories to

abolish customs duties and quantitative restrictions on the entry and outflow of merchandise, to abrogate all other measures having an equivalent effect, and to fix a common customs tariff for imports from nonmember states.

They also agreed to “abolish, as between members, all barriers to the free movement of persons, services and capital.”

The Treaty of Rome had set a timetable for the abolition of customs duties between member states. On balance, this timetable was met and in some areas exceeded so that, by the middle of 1968, tariff barriers had been abolished for agricultural as well as industrial products. By that date also, most quota restrictions had been lifted. The customs posts had not disappeared, however; they were still needed for such tasks as assessing and collecting the compensatory taxes that equalized the differences in taxes between member countries.

Tariffs on imports from outside the community were gradually brought closer, and on July 1, 1970, a common community tariff was put into effect.