The Spanish Civil War (Spanish: Guerra Civil Espaola) was a civil war in Spain fought from 1936 to 1939 between the Republicans and the Nationalists. Republicans were loyal to the left-leaning Popular Front government of the Second Spanish Republic. The Popular Front was constituted by the Spanish Socialist Workers' Party (PSOE), Communist Party of Spain (PCE), and the republicans Republican Left (IR) (led by Azaa) and Republican Union (UR) (led by Diego Martnez Barrio). This pact was supported by Galician (PG) and Catalan nationalists (ERC), the POUM, socialist union Workers' General Union (UGT), and the anarchist trade union, the Confederacin Nacional del Trabajo (CNT). Many anarchists who would later fight alongside Popular Front forces during the Spanish Civil War did not support them in the election, urging abstention instead. The Popular Front fought against an insurrection by the Nationalists, an alliance of Falangists, monarchists, conservatives and traditionalists, led by a military junta among whom General Francisco Franco quickly achieved a preponderant role. Due to the international political climate at the time, the war had many facets and was variously viewed as class struggle, a religious struggle, a struggle between dictatorship and republican democracy, between revolution and counterrevolution, and between fascism and communism. According to Claude Bowers, U.S. ambassador to Spain during the war, it was the "dress rehearsal" for World War II. The Nationalists won the war, which ended in early 1939, and ruled Spain until Franco's death in November 1975.

The war began after a pronunciamiento (a declaration of military opposition, of revolt) against the Republican government by a group of generals of the Spanish Republican Armed Forces, with General Emilio Mola as the primary planner and leader and having General Jos Sanjurjo as a figurehead. The government at the time was a coalition of Republicans, supported in the Cortes by communist and socialist parties, under the leadership of centre-left President Manuel Azaa. The Nationalist group was supported by a number of conservative groups, including CEDA, monarchists, including both the opposing Alfonsists and the religious conservative Carlists, and the Falange Espaola de las JONS, a fascist political party. After the deaths of Sanjurjo, Emilio Mola and Manuel Goded Llopis, Franco emerged as the remaining leader of the Nationalist side.

The coup was supported by military units in Morocco, Pamplona, Burgos, Zaragoza, Valladolid, Cdiz, Crdoba, and Seville. However, rebelling units in almost all important citiessuch as Madrid, Barcelona, Valencia, Bilbao, and Mlagadid not gain control, and those cities remained under the control of the government. This left Spain militarily and politically divided. The Nationalists and the Republican government fought for control of the country. The Nationalist forces received munitions, soldiers, and air support from Fascist Italy and Nazi Germany, while the Republican side received support from the Soviet Union and Mexico. Other countries, such as the United Kingdom, the French Third Republic, and the United States, continued to recognise the Republican government but followed an official policy of non-intervention. Despite this policy, tens of thousands of citizens from non-interventionist countries directly participated in the conflict. They fought mostly in the pro-Republican International Brigades, which also included several thousand exiles from pro-Nationalist regimes.

The Nationalists advanced from their strongholds in the south and west, capturing most of Spain's northern coastline in 1937. They also besieged Madrid and the area to its south and west for much of the war. After much of Catalonia was captured in 1938 and 1939, and Madrid cut off from Barcelona, the Republican military position became hopeless. Following the fall without resistance of Barcelona in January 1939, the Francoist regime was recognised by France and the United Kingdom in February 1939. On 5 March 1939, Colonel Segismundo Casado led a military coup against the Republican government. Following internal conflict between Republican factions in Madrid in the same month, Franco entered the capital and declared victory on 1 April 1939. Hundreds of thousands of Spaniards fled to refugee camps in southern France. Those associated with the losing Republicans who stayed were persecuted by the victorious Nationalists. Franco established a dictatorship in which all right-wing parties were fused into the structure of the Franco regime.The war became notable for the passion and political division it inspired and for the many atrocities that occurred. Organised purges occurred in territory captured by Franco's forces so they could consolidate their future regime. Mass executions on a lesser scale also took place in areas controlled by the Republicans, with the participation of local authorities varying from location to location.

The League of Nations (French: Société des Nations [sɔsjete de nɑsjɔ̃]) was the first worldwide intergovernmental organisation whose principal mission was to maintain world peace. It was founded on 10 January 1920 by the Paris Peace Conference that ended the First World War. The main organization ceased operations on 20 April 1946 but many of its components were relocated into the new United Nations.

The League's primary goals were stated in its Covenant. They included preventing wars through collective security and disarmament and settling international disputes through negotiation and arbitration. Its other concerns included labour conditions, just treatment of native inhabitants, human and drug trafficking, the arms trade, global health, prisoners of war, and protection of minorities in Europe. The Covenant of the League of Nations was signed on 28 June 1919 as Part I of the Treaty of Versailles, and it became effective together with the rest of the Treaty on 10 January 1920. The first meeting of the Council of the League took place on 16 January 1920, and the first meeting of Assembly of the League took place on 15 November 1920. In 1919 U.S. president Woodrow Wilson won the Nobel Peace Prize for his role as the leading architect of the League.

The diplomatic philosophy behind the League represented a fundamental shift from the preceding hundred years. The League lacked its own armed force and depended on the victorious First World War Allies (Britain, France, Italy and Japan were the permanent members of the Executive Council) to enforce its resolutions, keep to its economic sanctions, or provide an army when needed. The Great Powers were often reluctant to do so. Sanctions could hurt League members, so they were reluctant to comply with them. During the Second Italo-Ethiopian War, when the League accused Italian soldiers of targeting International Red Cross and Red Crescent Movement medical tents, Benito Mussolini responded that "the League is very well when sparrows shout, but no good at all when eagles fall out."At its greatest extent from 28 September 1934 to 23 February 1935, it had 58 members. After some notable successes and some early failures in the 1920s, the League ultimately proved incapable of preventing aggression by the Axis powers in the 1930s. The credibility of the organization was weakened by the fact that the United States never joined the League and the Soviet Union joined late and was soon expelled after invading Finland. Germany withdrew from the League, as did Japan, Italy, Spain and others. The onset of the Second World War in 1939 showed that the League had failed its primary purpose; it was inactive until its abolition. The League lasted for 26 years; the United Nations (UN) replaced it in 1946 and inherited several agencies and organisations founded by the League.