Two Sicilies with Swiss Guards present at the siege of Gaeta in 1860. An important clause of the constitution was that it could be entirely rewritten if necessary, thus enabling it to evolve as a whole rather than being modified one amendment at a time. This need soon proved itself when the rise in population and the Industrial Revolution that followed led to calls to modify the constitution accordingly. The population rejected an early draft in 1872, but modifications led to its acceptance in 1874. It introduced the facultative referendum for laws at the federal level. It also established federal responsibility for defence, trade, and legal matters. In 1891, the constitution was revised with unusually strong elements of direct democracy, which remain unique today. Modern history Switzerland was not invaded during either of the world wars. During World War I, Switzerland was home to the revolutionary and founder of the Soviet Union Vladimir Illych Ulyanov (Vladimir Lenin) who remained there until 1917. Swiss neutrality was seriously questioned by the short-lived Grimm–Hoffmann affair in 1917. In 1920, Switzerland joined the League of Nations, which was based in Geneva, after it was exempted from military requirements. During World War II, detailed invasion plans were drawn up by the Germans, but Switzerland was never attacked. Switzerland was able to remain independent through a combination of military deterrence, concessions to Germany, and good fortune, as larger events during the war intervened. General Henri Guisan, appointed the commander-in-chief for the duration of the war ordered a general mobilisation of the armed forces. The Swiss military strategy changed from static defence at the borders to organised long-term attrition and withdrawal to strong, well-stockpiled positions high in the Alps, known as the Reduit. Switzerland was an important base for espionage by both sides and often mediated communications between the Axis and Allied powers. Switzerland's trade was blockaded by both the Allies and the Axis. Economic cooperation and extension of credit to Nazi Germany varied according to the perceived likelihood of invasion and the availability of other trading partners. Concessions reached a peak after a crucial rail link through Vichy France was severed in 1942, leaving Switzerland (together with Liechtenstein) entirely isolated from the wider world by Axis-controlled territory. Over the course of the war, Switzerland interned over 300,000 refugees aided by the International Red Cross, based in Geneva. Strict immigration and asylum policies and the financial relationships