After the
armistice of 11 November 1918, German troops left the country, making way for the Allied armies which passed through Luxembourg to occupy the
Rhineland.
Economic partner Germany's defeat rendered Luxembourg's existing treaties obsolete. After the French announcement, the Luxembourgish government re-started negotiations with Belgium. These were slow-going, but resulted on 25 July 1921 in the signing of a treaty on a customs and monetary union between the two countries. The
Belgium–Luxembourg Economic Union came into force in March 1922. The treaty stipulated the abolition of customs barriers between the two countries, a
common external tariff, a common trade policy led by Belgium and a currency association. The
Belgian franc became the common currency, while Luxembourg however retained its right to print Luxembourgish notes. The economic union was never a perfect one, as the treaty did not require the harmonisation of tax systems.
League of Nations Bound by its neutral status and solidly anchored in the German sphere of influence, Luxembourg had not led a real foreign policy before World War I. The violation of its neutrality in 1914 and the questioning of its independence during 1918-1919 showed the Luxembourgish government that it was necessary to play a role on the international stage. Luxembourg was not invited to the
Paris Peace Conference and was not one of the founding members of the
League of Nations established by the
Treaty of Versailles. From 1919, the Reuter government took steps to have the Grand Duchy admitted to the League of Nations. Luxembourg's unarmed neutrality seemed at first to present an obstacle to its admission, as the League's charter provided for the passage of troops over member states' territory, and the participation in economic and financial sanctions against a hypothetical belligerent. At the same time, the United Kingdom considered the small size of Luxembourg's territory a problem. The Reuter government succeeded in overcoming these objections, partly by hinting at the possibility of a revision of the Luxembourgish Constitution. On 16 December 1920, a session of the League of Nations in Geneva voted unanimously to have Luxembourg admitted. Later, the Luxembourgish government, conscious of the population's attachment to the principle of neutrality, let the constitutional revision drag on; it would never come into force. == Domestic policy ==