French Third Republic in the context of "Invasion of Poland"

The Allies, formally referred to as the United Nations from 1942, were an international military coalition formed during World War II (1939–1945) to oppose the Axis powers. Its principal members were the "Big Four" – the United Kingdom, Soviet Union, United States, and China.

Membership in the Allies varied during the course of the war. When the conflict broke out on 1 September 1939, the Allied coalition consisted of the United Kingdom, France, and Poland, as well as their respective dependencies, such as British India. They were joined by the independent dominions of the British Commonwealth: Canada, Australia, New Zealand and South Africa. Consequently, the initial alliance resembled that of the First World War. As Axis forces began invading northern Europe and the Balkans, the Allies added the Netherlands, Belgium, Norway, Greece, and Yugoslavia. The Soviet Union, which initially had a nonaggression pact with Germany and participated in its invasion of Poland, joined the Allies after the German invasion of the Soviet Union in June 1941. The United States, while providing some material support to European Allies since September 1940, remained formally neutral until the Japanese attack on Pearl Harbor in December 1941, after which it declared war and officially joined the Allies. China had already been at war with Japan since 1937, and formally joined the Allies in December 1941.

The Spanish Civil War (Spanish: guerra civil española) was 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 and included socialists, anarchists, communists, and separatists. The opposing Nationalists who established the Spanish State were an alliance of fascist Falangists, monarchists, conservatives, and traditionalists supported by Nazi Germany and Fascist Italy and 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 was variously viewed as class struggle, a religious struggle, or a struggle between dictatorship and republican democracy, between revolution and counterrevolution, or between fascism and communism. The Nationalists won the war, which ended in early 1939, and ruled Spain until Franco's death in November 1975.

The war began after the partial failure of the coup d'état of July 1936 against the Popular Front government by a group of generals of the Spanish Republican Armed Forces. The Nationalist faction consisted of right-wing groups, including Christian traditionalist party CEDA, monarchists, including both the opposing Alfonsists and the religious conservative Carlists, and the Falange Española de las JONS, a fascist political party. However, rebelling units in almost all important cities did not gain control, leaving Spain militarily and politically divided. The rebellion was countered with the help of arming left-wing social movements and parties and formation of militias, what led to rapid socioeconomic and political transformation in the Republican zone, referred to as the Spanish Revolution. 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, France, 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, mostly in the pro-Republican International Brigades.

The Munich Agreement was reached in Munich on 30 September 1938, by Nazi Germany, the United Kingdom, France, and Italy. The agreement provided for the German annexation of part of Czechoslovakia called the Sudetenland, where three million people, mainly ethnic Germans, lived. The pact is known in some areas as the Munich Betrayal (Czech: Mnichovská zrada; Slovak: Mníchovská zrada), because of a previous 1924 alliance agreement and a 1925 military pact between France and the Czechoslovak Republic.

Germany had started a low-intensity undeclared war on Czechoslovakia on 17 September 1938. In reaction, Britain and France on 20 September formally requested Czechoslovakia cede the Sudetenland territory to Germany. This was followed by Polish and Hungarian territorial demands brought on 21 and 22 September, respectively. Meanwhile, German forces conquered parts of the Cheb District and Jeseník District, where battles included use of German artillery, Czechoslovak tanks, and armored vehicles. Lightly armed German infantry briefly overran other border counties before being repelled. Poland grouped its army units near its common border with Czechoslovakia and conducted an unsuccessful probing offensive on 23 September. Hungary moved its troops towards the border with Czechoslovakia, without attacking. The Soviet Union announced its willingness to come to Czechoslovakia's assistance, provided the Red Army would be able to cross Polish and Romanian territory; both countries refused.

On 3 September 1939—two days after the German invasion of Poland—France declared war on Nazi Germany according to its defensive treaty with Poland, when France's ultimatum to Germany, issued the previous day, expired at 17:00. This occurred hours after the United Kingdom declaration of war on Germany.

Between 28 June and 3 July 1940, the Soviet Union occupied Bessarabia and Northern Bukovina, following an ultimatum made to Romania on 26 June 1940 that threatened the use of force. Those regions, with a total area of 50,762 km (19,599 sq mi) and a population of 3,776,309 inhabitants, were incorporated into the Soviet Union. On 26 October 1940, six Romanian islands on the Chilia branch of the Danube, with an area of 23.75 km (9.17 sq mi), were also occupied by the Soviet Army.

The Soviet Union had planned to accomplish the annexation with a full-scale invasion, but the Romanian government, responding to the Soviet ultimatum delivered on 26 June, agreed to withdraw from the territories to avoid a military conflict. The use of force had been made illegal by the Conventions for the Definition of Aggression in July 1933, but from an international legal standpoint, the new status of the annexed territories was eventually based on a formal agreement through which Romania consented to the retrocession of Bessarabia and cession of Northern Bukovina. As it was not mentioned in the ultimatum, the annexation of the Hertsa region was not consented to by Romania, and the same is true of the subsequent Soviet occupation of the Danube islands. On 24 June, Nazi Germany, which had acknowledged the Soviet interest in Bessarabia in a secret protocol to the 1939 Molotov–Ribbentrop Pact, had been made aware prior to the planned ultimatum but did not inform the Romanian authorities and was unwilling to provide support. On 22 June, France, a guarantor of Romanian borders, fell to Nazi advances. This is considered to be an important factor in the Soviets' decision to issue the ultimatum. The Soviet invasion of Bukovina in 1940 violated the Molotov-Ribbentrop Pact, since it went beyond the Soviet sphere of influence that had been agreed with the Axis.

The Battle of France (French: bataille de France; 10 May – 25 June 1940), also known as the Western Campaign (German: Westfeldzug), the French Campaign (Frankreichfeldzug, campagne de France) and the Fall of France, during the Second World War was the German invasion of the Low Countries (Belgium, Luxembourg and the Netherlands) and France. The plan for the invasion of the Low Countries and France was called Fall Gelb (Case Yellow or the Manstein plan). Fall Rot (Case Red) was planned to finish off the French and British after the evacuation at Dunkirk. The Low Countries and France were defeated and occupied by Axis troops down to the Demarcation line.

On 3 September 1939, France and Britain declared war on Nazi Germany, over the German invasion of Poland on 1 September. In early September 1939, the French army began the limited Saar Offensive but by mid-October had withdrawn to the start line. On 10 May 1940, Wehrmacht armies invaded Belgium, Luxembourg, the Netherlands and parts of France.

The Mediterranean and Middle East theatre, also known as the Mediterranean Theater of War, was a major theatre of operations during the Second World War. The vast size of the theatre saw interconnected land, naval, and air campaigns fought for control of the Mediterranean Sea, North Africa, the Horn of Africa, the Middle East and Southern Europe. Despite their disparate geographic locations and objectives, these operations were not seen as neatly separated from each other, but part of an extensive, contiguous theatre of war.

The Mediterranean theater had the longest duration of the Second World War. Combat started on 10 June 1940 with Italy's declaration of war against the United Kingdom and France and ended on 2 May 1945 when all Axis forces in Italy surrendered. In Germany military history, the scope of the theatre is described as Mediterranean, South-East Europe, and North Africa 1939–1941. Additionally, various post-war conflicts, such as the Greek Civil War and the first phase of the Palestine War, were rooted in events during the Mediterranean theater.

The unequal treaties were a series of agreements made between Asian countries—most notably Qing China, Tokugawa Japan and Joseon Korea—and Western countries—most notably the United Kingdom, France, Germany, Austria-Hungary, Italy, the United States and Russia—during the 19th and early 20th centuries. They were often signed following a military defeat suffered by the Asian party, or amid military threats made by the Western party. The terms specified obligations to be borne almost exclusively by the Asian party and included provisions such as the cession of territory, payment of reparations, opening of treaty ports, relinquishment of the right to control tariffs and imports, and granting of extraterritoriality to foreign citizens.

With the rise of Chinese nationalism and anti-imperialism in the 1920s, both the Kuomintang and the Chinese Communist Party used the concept to characterize the Chinese experience of losing sovereignty between roughly 1840 to 1950. The term "unequal treaty" became associated with the concept of China's "century of humiliation", especially the concessions to foreign powers and the loss of tariff autonomy through treaty ports, and continues to serve as a major impetus for the foreign policy of China today.

The Treaty of Lausanne (French: Traité de Lausanne, Turkish: Lozan Antlaşması) is a peace treaty negotiated during the Lausanne Conference of 1922–1923 and signed in the Palais de Rumine in Lausanne, Switzerland, on 24 July 1923. The treaty officially resolved the conflict that had initially arisen between the Ottoman Empire and the Allied French Republic, British Empire, Kingdom of Italy, Empire of Japan, Kingdom of Greece, Kingdom of Serbia, and the Kingdom of Romania since the outset of World War I. The original text of the treaty is in English and French. It emerged as a second attempt at peace after the failed and unratified Treaty of Sèvres, which had sought to partition Ottoman territories. The earlier treaty, signed in 1920, was later rejected by the Turkish National Movement which actively opposed its terms. As a result of Greek defeat in the Greco-Turkish War, Turkish forces recaptured İzmir, and the Armistice of Mudanya was signed in October 1922. This armistice provided for the exchange of Greek-Turkish populations and allowed unrestricted civilian, non-military passage through the Turkish Straits.

Turkey ratified the treaty on 23 August 1923, and all other signatories did so by 16 July 1924. The Treaty of Lausanne became effective on 6 August 1924.