by @Chris
Who held which land, from the shots in Sarajevo (28 June 1914) to the end of 1919, in 34 keyframes. Central Powers are warm colours (Germany, Austria-Hungary, the Ottoman Empire, Bulgaria), the Allies cool colours, and countries are grey while neutral; pale tints mark land occupied by a foreign army (German-occupied Belgium, Russian-occupied Galicia, British-occupied Mesopotamia …). Every front is followed — the Western Front, the Eastern Front and the Great Retreat, the Isonzo and the Piave, Serbia and Salonika, Romania, Gallipoli, the Caucasus, Mesopotamia, Palestine and the Arab Revolt — and then the collapse of four empires: Brest-Litovsk, the armistices, the new states from Finland to the Kingdom of Serbs, Croats and Slovenes, the Allied Rhineland, the Polish, Baltic, Hungarian and Russian wars and the treaties of 1919. Russia is shown west of the Urals; Persia and the Arabian interior are not shaded. Borders: Natural Earth units cut by historical lines from OpenHistoricalMap (CC0), treaty texts and official histories; front lines are approximate (about 2–10 km, more in deserts and in the Russian Civil War).
German Empire (Germany from Nov 1918) · Occupied by Germany (Western Front) · Austria-Hungary: Austrian lands · Ottoman Empire · Occupied by the Ottomans and their allies · Bulgaria · Occupied by Germany (East and Balkans) · Austria-Hungary: Kingdom of Hungary (with Croatia) · Austria-Hungary: Bosnia-Herzegovina · Occupied by Austria-Hungary · Ottoman Empire: Arab provinces · Occupied by Bulgaria · France · Occupied by France · British Empire (UK and Ireland) · British Egypt, Cyprus and Kuwait · Occupied by Britain · Russian Empire (Russian Republic from 1917) · Russian Empire: Grand Duchy of Finland · Russian Empire: Caucasus · Occupied by Russia · Italy · Occupied by Italy · Serbia (Kingdom of Serbs, Croats and Slovenes from Dec 1918) · Occupied by Serbia / Yugoslavia · Occupied by Belgium · Occupied by the United States · Romania · Montenegro · Belgium · Occupied by Romania · Greece · Greece – Venizelist Provisional Government (1916–17) · Occupied by Greece · Portugal · Allied (multinational) occupation · Neutral countries · Luxembourg (neutral) · Albania · Soviet Russia and Soviet republics · Anti-Bolshevik (White) Russia · Finland · Estonia · Latvia · Lithuania · Poland · Ukraine (People’s Republic, Hetmanate, Directorate) · West Ukrainian People’s Republic · Czechoslovakia · German-Austria (Austria) · Hungary · State of Slovenes, Croats and Serbs (Oct–Dec 1918) · Transcaucasian Commissariat / Federation · Georgia · Armenia · Azerbaijan · Mountain Republic of the North Caucasus · Hejaz (Arab Revolt) · Arab government in Damascus · Other local governments and insurgents