In 1867, Prussia and France were on the brink of war over Luxembourg, as both nations sought to keep the city and its fortress within their respective spheres of influence. An international conference was convened to avert a conflict on the European continent and to find a peaceful solution to what became known as the ‘Luxembourg Crisis’. This conference resulted in the signing of the Treaty of London on 11 May 1867, which stipulated that Luxembourg would retain its independence while remaining in a personal union with the Kingdom of the Netherlands. At the same time, the country was declared demilitarised and perpetually neutral. Article 1 of the Luxembourg Constitution of 1868 incorporated the provision of perpetual neutrality. The Great Powers of Europe that signed the treaty—namely Prussia, France, Great Britain, Austria, Russia, and Italy—pledged to collectively guarantee Luxembourg’s security, and German troops were required to evacuate the fortress. As a result of the treaty, the fortress was gradually dismantled, a process that took sixteen years, from 1867 to 1883. Subsequently, neutrality became a state doctrine—notably under Prime Minister Paul Eyschen—and was embraced by the population as a distinctive feature of its country. Luxembourg was soon portrayed as a haven or an island of peace.

The peaceful resolution of the Luxembourg Crisis failed to prevent war between Paris and Berlin. When the Franco-Prussian conflict broke out in July 1870, Luxembourg’s neutrality was put to the test. Several major battles took place near the Franco-Luxembourgish border, and although both belligerents had pledged to respect this neutral territory, the population feared that the fighting would spill over into the Grand Duchy. Ultimately, the country was spared.

To demonstrate Luxembourg’s value as a neutral state, a citizen initiative was launched to aid wounded soldiers from both sides. Doctors and nurses went to the battlefields to provide relief to the victims of the war. This initiative is considered a precursor to the founding of the Luxembourg Red Cross in 1914. Due to these humanitarian missions in France and the widespread francophile sentiment within the Grand Duchy, Germany accused Luxembourg of failing to uphold its obligations of neutrality.

The First World War began with the German invasion of Luxembourg and Belgium—two neutral states—on 2 and 4 August 1914. Although Germany was a signatory to the Treaty of London, this did not prevent it from violating Luxembourg’s neutrality in the name of its own security interests. Due to this violation, the treaty was described as nothing more than a ‘scrap of paper’. While Luxembourg protested the violation of its neutrality, it also sought to reach a modus vivendi with the German Empire, which occupied the country until the war ended in 1918.

Following the armistice, Luxembourg maintained its policy of neutrality. It was only after a second invasion on 10 May 1940—this time by Nazi Germany—that Luxembourg altered its foreign policy stance: the government-in-exile aligned itself with the Allied forces and introduced compulsory military service for male citizens in 1944. A year later, the country joined NATO as a founding member. In effect, Luxembourg had abandoned its neutrality. This policy shift was formalised in 1948 when the provision for neutrality was removed from the Constitution.