The Battle of Cambrai (Battle of Cambrai, 1917, First Battle of Cambrai and Schlacht von Cambrai) was a British attack in the First World War, followed by the biggest German counter-attack against the British Expeditionary Force (BEF) since 1914. The town of Cambrai, in the dpartement of Nord, in France, was an important supply centre for the German Siegfriedstellung (known to the British as the Hindenburg Line) and capture of the town and the nearby Bourlon Ridge would threaten the rear of the German line to the north. Major General Henry Tudor, Commander, Royal Artillery (CRA), of the 9th (Scottish) Division, advocated the use of new artillery-infantry tactics on his sector of the front. During preparations, J. F. C. Fuller, a staff officer with the Tank Corps, looked for places to use tanks for raids. General Julian Byng, commander of the Third Army, decided to combine both plans. The French and British armies had used tanks en masse earlier in 1917, although to considerably less effect.After a big British success on the first day, mechanical unreliability, German artillery and infantry defences exposed the frailties of the Mark IV tank. On the second day, only about half of the tanks were operational and British progress was limited. In the History of the Great War, the British official historian Wilfrid Miles and modern scholars do not place exclusive credit for the first day on tanks but discuss the concurrent evolution of artillery, infantry and tank methods. Numerous developments since 1915 matured at Cambrai, such as predicted artillery fire, sound ranging, infantry infiltration tactics, infantry-tank co-ordination and close air support. The techniques of industrial warfare continued to develop and played a vital part during the Hundred Days Offensive in 1918, along with replacement of the Mark IV tank with improved types. The rapid reinforcement and defence of Bourlon Ridge by the Germans, as well as their counter-attack, were also notable achievements, which gave the Germans hope that an offensive strategy could end the war before American mobilisation became overwhelming.

World War I, often abbreviated as WWI or WW1, also known as the First World War and contemporaneously known as the Great War and by other names, was an international conflict that began on 28 July 1914 and ended on 11 November 1918. It involved much of Europe, as well as Russia, the United States and Turkey, and was also fought in the Middle East, Africa and parts of Asia. One of the deadliest conflicts in history, an estimated 9 million were killed in combat, while over 5 million civilians died from occupation, bombardment, hunger or disease. The genocides perpetrated by the Ottomans and the 1918 Spanish flu pandemic spread by the movement of combatants during the war caused many millions of additional deaths worldwide.In 1914, the Great Powers were divided into two opposing alliances: the Triple Entente, consisting of France, Russia, and Britain, and the Triple Alliance, made up of Germany, Austria-Hungary, and Italy. Tensions in the Balkans came to a head on 28 June 1914 following the assassination of Archduke Franz Ferdinand, the Austro-Hungarian heir, by Gavrilo Princip, a Bosnian Serb. Austria-Hungary blamed Serbia and the interlocking alliances involved the Powers in a series of diplomatic exchanges known as the July Crisis. On 28 July, Austria-Hungary declared war on Serbia; Russia came to Serbia's defence and by 4 August, the conflict had expanded to include Germany, France and Britain, along with their respective colonial empires. In November, the Ottoman Empire, Germany and Austria formed the Central Powers, while in April 1915, Italy joined Britain, France, Russia and Serbia as the Allied Powers.

Facing a war on two fronts, German strategy in 1914 was to defeat France, then shift its forces to the East and knock out Russia, commonly known as the Schlieffen Plan. This failed when their advance into France was halted at the Marne; by the end of 1914, the two sides faced each other along the Western Front, a continuous series of trench lines stretching from the Channel to Switzerland that changed little until 1917. By contrast, the Eastern Front was far more fluid, with Austria-Hungary and Russia gaining, then losing large swathes of territory. Other significant theatres included the Middle East, the Alpine Front and the Balkans, bringing Bulgaria, Romania and Greece into the war.

Shortages caused by the Allied naval blockade led Germany to initiate unrestricted submarine warfare in early 1917, bringing the previously neutral United States into the war on 6 April 1917. In Russia, the Bolsheviks seized power in the 1917 October Revolution and made peace in the March 1918 Treaty of Brest-Litovsk, freeing up large numbers of German troops. By transferring these to the Western Front, the German General Staff hoped to win a decisive victory before American reinforcements could impact the war, and launched the March 1918 German spring offensive. Despite initial success, it was soon halted by heavy casualties and ferocious defence; in August, the Allies launched the Hundred Days Offensive and although the German army continued to fight hard, it could no longer halt their advance.Towards the end of 1918, the Central Powers began to collapse; Bulgaria signed an Armistice on 29 September, followed by the Ottomans on 31 October, then Austria-Hungary on 3 November. Isolated, facing revolution at home and an army on the verge of mutiny, Kaiser Wilhelm abdicated on 9 November and the new German government signed the Armistice of 11 November 1918, bringing the fighting to a close. The 1919 Paris Peace Conference imposed various settlements on the defeated powers, the best known being the Treaty of Versailles. The dissolution of the Russian, German, Ottoman and Austro-Hungarian empires led to numerous uprisings and the creation of independent states, including Poland, Czechoslovakia and Yugoslavia. For reasons that are still debated, failure to manage the instability that resulted from this upheaval during the interwar period ended with the outbreak of World War II in 1939.