| Historical period | Events |
| Austro-Hungarian invasion 1914 |
- 28 July [O.S. 15 July] 1914: Austria-Hungary declares war on Serbia, following the assassination of Archduke Franz Ferdinand of Austria. World War I begins with the bombing of Belgrade in the evening of the same day. Dušan Đonović falls as the first victim of the warfare.
- 2 December 1914: Austrians bombard and occupy Belgrade.
- 15 December 1914: The Serbs liberate Belgrade.
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| Austro-Hungarian occupation 1915–18 |
- 6–9 October 1915: German and Austrian troops led by August von Mackensen re-occupy Belgrade. Colonel Dragutin Gavrilović sacrifices the entire legion for the city.
- 1 November 1918: The Serbs liberate Belgrade.
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| Kingdom of Serbia 1918 |
- 24 November 1918: The Assembly of Syrmia proclaims the secession of Syrmia from the State of Slovenes, Croats and Serbs and unification with the Kingdom of Serbia, thus unifying Belgrade with Zemun in the same state.
- 25 November 1918: The Great people's assembly of Serbs, Bunjevci and other Slavs proclaims the unification of Banat, Bačka and Baranja with the Kingdom of Serbia, thus unifying Belgrade and the settlements on the Danube's left bank in the same state.
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| Kingdom of Yugoslavia 1918–1941 |
- 1 December 1918: Belgrade becomes the capital of the Kingdom of Serbs, Croats and Slovenes. The document was signed at Krsmanović's House at Terazije.[16]
- 28 January [O.S. 15 January] 1919: In order to coordinate the dating in different parts of the newly formed state, the territories of former Serbia and Montenegro adopt Gregorian calendar, which had already been in use in the other parts of the kingdom.
- 1923: Paris–Budapest air line extended to Belgrade.
- 25 March 1927: The first Belgrade airport (Dojno polje Airport) opened.
- 6 January 1929: King Aleksandar Karađorđević dissolved the National Assembly and started his dictatorship. Belgrade becomes the capital of the Kingdom of Yugoslavia.
- 24 March 1929: Radio Belgrade started broadcasting.
- 1 April 1934: Zemun annexed to the City of Belgrade.
- 27 October 1935: The first bridge over the Danube, the Pančevački most (Bridge of Pančevo) is built.
- 11 September 1937: Belgrade Fair opened.
- 20 May 1938: Drying out of the wetland on the Sava's left bank begins, making place for the future New Belgrade.
- 14 December 1939: Leftist students' protests against the government, poverty and war. During the police breakdown of the demonstrations, five to ten protesters are killed (depending on the sources).
- 27 March 1941: Huge protests against joining the Axis.
- 6–8 April 1941: Nazi Germany bombs Belgrade (Operation Retribution). 2,271–4,000 casualties, depending on the sources. Many public and private buildings completely destroyed, including the building of the National Library of Serbia, along with an invaluable collection of books, manuscripts, charters, old maps, journals and many other documents. The Royal Yugoslav Army, while retreating, destroys all the bridges crossing Sava and Danube.
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| Nazi German occupation 1941–1944 |
- 12 April 1941: Belgrade is occupied by German forces.
- April 1941 – October 1944: Belgrade is occupied and divided. Old part of the city becomes a part of Nazi Germany and the capital of the Territory of the Military Commander in Serbia, governed by puppet Government of National Salvation. The settlements on the Danube's left bank become a part of the Banat autonomous region, formally responsible to the puppet governments in Belgrade, but in practice governed by its Volksdeutsche (ethnic German) minority, while Zemun becomes a part of the Independent State of Croatia. Four concentration camps have operated on the territory of the occupied Belgrade: Sajmište, Banjica, Topovske Šupe, and Milišić's brickyard. Approximately 50,000 people have died in these camps, most of them in Sajmište concentration camp, on the territory controlled by the Independent State of Croatia.
- 1942: The Germans, using forced labour, build Old Sava Bridge.
- April–September 1944: The Allies have bombed Belgrade eleven times. 1,000 – 5,000 civilian casualties, depending on the sources.
- 14 September 1944 – 24 November 1944: Belgrade Offensive by the units of the Soviet Red Army and the Yugoslav Partisans. The main battles in the Belgrade's urban area took place 28 September 1944 – 20 October 1944.
- 20 October 1944: Liberation of Belgrade. Miladin Zarić, an ordinary citizen, saves Old Sava Bridge from demolition, by cutting the detonator wires, making it the only large bridge in Europe, beside Ludendorff Bridge, that the Germans didn't succeed in demolishing while retreating. This way, the Soviet troops manage to cross Sava river and to definitely expel the Germans from the city.
- 22 October 1944: Liberation of Zemun.
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