The siege of Antwerp (Dutch: Beleg van Antwerpen, French: Sige d'Anvers, German: Belagerung von Antwerpen) was an engagement between the German and the Belgian, British and French armies around the fortified city of Antwerp during World War I. German troops besieged a garrison of Belgian fortress troops, the Belgian field army and the British Royal Naval Division in the Antwerp area, after the German invasion of Belgium in August 1914. The city, which was ringed by forts known as the National Redoubt, was besieged to the south and east by German forces.

The Belgian forces in Antwerp conducted three sorties in late September and early October, which interrupted German plans to send troops to France, where reinforcements were needed to counter the French armies and the British Expeditionary Force (BEF). A German bombardment of the Belgian fortifications with heavy and super-heavy artillery began on 28 September. The Belgian garrison had no hope of victory without relief and despite the arrival of the Royal Naval Division beginning on 3 October the Germans penetrated the outer ring of forts. When the German advance began to compress a corridor from the west of the city along the Dutch border to the coast, through which the Belgians at Antwerp had maintained contact with the rest of unoccupied Belgium, the Belgian Field Army commenced a withdrawal westwards towards the coast.

On 9 October, the remaining garrison surrendered, the Germans occupied the city and some British and Belgian troops escaped to the Netherlands to the north and were interned for the duration of the war. Belgian troops from Antwerp withdrew to the Yser river, close to the French border and dug in, to begin the defence of the last unoccupied part of Belgium and fought the Battle of the Yser against the German 4th Army in October and November 1914. The Belgian Army held the area until late in 1918, when it participated in the Allied liberation of Belgium.

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.