The assassination of Archduke Franz Ferdinand in Sarajevo in 1914 started the Great War of 1914 - 1919, through various treaties between the nations of Europe, most European countries were involved.
On the side of the Central Powers were:
- The German Empire and colonies.
- Austro-Hungarian Empire (Succeeded by Federal Republic of Austria-Hungary in 1917)
- The Kingdom of Italy and colonies. (1914 - 1916)
- Islamic Emirate of Albania (1916 - ) (unrecognised by all non - Central Powers countries)
- Kingdom of Yemen (1915 - 1916)
- Shahdom of Persia (1915 - 1916)
- Kingdom of Greece (1914 - 1916)
- Grand Duchy of Poland (German puppet state in German-controlled Poland)
On the side of the Allied Powers were:
- British Empire and colonies.
- Republic of France and colonies.
- Kingdom of Serbia
- Republic of Bulgaria
- Kingdom of Romania
- Russian Empire
- Kingdom of Albania-Montenegro
- Sultanate of Oman (1915 - )
- Kingdom of Italy (1916 - )
- Empire of Japan
- Republic of Portugal
- Kingdom of Belgium
- Empire of Ethiopia
- Hellenic Republic (1916 - )
When the war started, Russia immediately mobilised its huge army and invaded Austrian Galicia and German East Prussia. The battles of Stalluponen, Gumbinnen and Tannenberg resulted in Russian victories, but the enormous casualty figures at Tannenberg made the Tsar sack General Aleksandr Samsonov and replace him with General Brusilov, hero of the Russo - Japanese War.
Further south, in Galicia the city of Lemberg (Lviv) had been taken by the Russians from the Austrians, however the Russians lost the battle of Krasnik in southern Poland to a larger Austrian army. While in the north The Battle of the Mausurian Lakes ended in stalemate.
By early 1915 the Western front had become a complete stalemate, so to secure victory, decisive wins on the Eastern Front would be required. In the Middle East, Germany gained two new allies, Persia and North Yemen, Yemeni forces invaded Britain's Aden Protectorate, while Persia invaded Russian Azerbaijan. British forces in Aden counter-attacked and along with Omani troops had, by early 1916 captured the whole of Yemen and the new Yemen Protectorate was proclaimed. In Persia, Russian troops under Nikolai Yudenitch invaded from the north, while British Indian forces attacked from the south, in mid 1916 they reached Tehran and the Shah was deposed and replaced by his pro-Western son. Although Serbia repelled an Austrian invasion in late 1914, it could not withstand a combined Greek, German and Austrian invasion in 1915, most of its army fled to Bulgaria along with the royal family. Montenegro was invaded and due to its small size could not fight off the invasion, The royal family and most of the army fled south, and along with a British force, took Corfu, and set up a Government in Exile.
When Italy joined the Central Powers in 1914, it immediately came under attack from France to the west, its isolated colonies were vulnerable, Libya was invaded and taken by an Anglo-Egyptian force, while Eritrea and Italian Somaliland were invaded by Portuguese and Ethiopian troops. On the day French troops captured Genoa, King Vittorio dissolved parliament and declared war on the Central Powers, Italian troops opened a second front with Austria in Tyrolia.
On the eastern front, Russia besieged and captured the important fortress of Przemysl, while a German offensive in Poland was halted at the Vistula River, a second offensive was halted at the 2nd Battle of the Mausurian Lakes, but the Russian counter-offensive was also halted. In the south, Russia's ally Romania had been almost overrun, except for the region of Moldavia in the north east, although Bulgaria was continuing to resist Austrian and Greek attacks. An attack for early 1916 was formulated, in which Brusilov would attack Central Powers troops in Romania and attempt to reach Bulgaria, while Allied troops would land in Greece, with the aim of knocking it out of the war.
In Europe, the Western and Italian fronts were stalemated and bloody, but the Eastern front was still fluid. The planned offensive for 1916 took place, Brusilov's attack suceeded in liberating Romania, Austrian commander von Hotzendorf surrendered to Brusilov when Bucharest fell. The Austrian army lost almost a million men killed or captured in this campaign and the subsequent offensive in Galicia, Russian troops entered Hungary itself and and foothills of the Carpathians. The Romanian royal family was restored to the throne.
In Greece an allied force force of French, Portuguese, Italian, British and Indian troops landed, Athens was taken bloodlessly and King George deposed and the Hellenic Republic was proclaimed and Leonidas Paraskevopoulos was named president, the allied forces began advancing northwards, by the end of the year, the Islamic Emirate of Albania had been destroyed and the Montenegrin King took up residence in Tirana until Montenegro could be liberated.
By late 1916 Austria-Hungary was in trouble, its inept armies were losing on every front and in November Emperor Franz Josef died, he was succeeded by Emperor Charles, who reigned for just over a month before he was overthrown amid riots in Vienna and mass desertion from the armies. The Federal Republic of Austria - Hungary was proclaimed, the new government of Karl Renner continued the war, which was deeply unpopular.
In June 1917 the Italians made a breakthrough in Tyrolia, the Russians were deep into Hungary and by September and the Allies had taken Belgrade and liberated Montenegro.
The war dragged on for a few more months until March 1919 when, after growing unrest in Germany over food shortages the Kaiser was overthrown and the new government asked for peace. Seeing this, the remaining Central Powers, Austria Hungary asked for peace. On 6th January 1920 the Treaty of Copenhagen ended the war officially.