In 1948 a Custom's Union was established between Belgium, the Netherlands and Luxembourg, restrictions on internal trade were removed and a common external tariff was applied. With regards to agriculture imports of agricultural products from other Benelux countries as well as from third countries could be restricted so far as necessary to maintain minimum prices, however preference was to be given to supplies from the Benelux. The experience for agriculture was not successful. In 1950 a study was carried out by the Consultative Assembly of the Council of Europe, it led to the Charpentier proposal which put forward the idea of a high authority for agriculture based on the Schuman Plan's proposal for Coal and Steel. The supranational aspect of the plan was opposed in the subsequent Eccles Plan, however despite opposition the Special Committee of Agriculture adopted the Charpentier Plan. In the meantime a similiar plan was proposed by the French Minister for Agriculture which bore his name, the Pflimlin Plan, another plan was proposed by the Dutch Minister for Agriculture, Sicco Mansholt, again this plan bore his name, the Mansholt Plan. As a result of these proposals, conferences were convened on the Organisation of European Agricultural Market, which took place in Paris between 1952-54, however nothing came out of them. The OEEC was also actively involved in attempts to integrate agricultural policies among its members, the Ministerial Committee for Agriculture and Food was established in 1955. These various movements helped to raise the issues concerning basic problems of Western European agriculture at the time.
The Spaak report which formed the basis of the Treaties establishing the EEC and the European Atomic Energy Community, was very ambiguous with regard to agriculture, which reflected the basic state of agriculture in Europe, however it gave a mandate to the Community institutions to develop a policy for agriculture, which came to be known as the Common Agricultural Policy.

See Michael Tracy's book: Government and Agriculture in Western Europe 1880-1988, 3rd ed. (1989)