On 17 February 1914 Austria declares war on Dalmatian Hercegovina after DH rejected the Austrian Ultimatum. Following the Austrian declaration, on 20 February the other two members of the Triple Entente declare war on Austria, thus bringing the Balkans into the First Great War.

Subsequently, in April 1914, Hungary, who were the first to throw the Turk off in 1869 declared war on Muntenia and by proxy Dalmatian Hercegovina and the Two Sicilies. Hungary and Austria were on fairly good terms before the war broke out and the Hungarians always had designs on Muntenian territory, so this general war provided an excellent excuse for the Hungarians to make a move.

Montenegro, who gained independence in 1883 from the Turk, declared war on the Triple Entente in June 1914, after the Austrians promised certain Hercegovian lands to them. The Montenegrin attacks the Two Sicilies in Albania.

The Turk, who is still in Europe though holding on only to Greece, also sides with Austria in September 1914, hoping to regain some of the territories she lost.

A few days after the Turkish entry into the war, Bulgaria declares war on Turkey at the behest of the Triple Entente.

Russia does not stay uninvolved. Seeing an opportunity, the Russians invade Hungary, to draw Hungarian attention away from Dalmatia, and open a second front for the Hungarians, who are forced to concentrate on the greater Russian threat, leaving them less able to deal with the Muntenians. This enables the Oltenians, at this point under Hungarian rule, to open an internal front and openly revolt against the Hungarian crown late 1915.

The battle between the Bulgarians and the Turks quickly turns into a war of attrition over lines that rarely, if ever, move; basically, they are shooting at each other over the pre-war borders. As this intensifies, the Turks are forced to attend to this front more and concentrate less on defending their border with Albania.

The Two Sicilies, together with Dalmatia, quickly crush the Montenegrin after the Hungarians are forced to more or less withdraw from the southern front after the Oltenians rebel and the Russian invasion of Hungary, allowing the Dalmatians to send some units south (Muntenians cover for them against Austria. After the fall of Montenegro, its territory is assimilated into Dalmatian Hercegovina, though there were a few skirmishes with Sicilian forces, but nothing significant).

Inside Austria, the Slovenes fight loyally to the Austrian Crown. The Serbs are considered as having "questionable" loyalty: upon arriving at the front, many surrendered at the earliest convenience, or just acting like the famous hero of the novel by Borislav Hašković, The Good Soldier Švejković and his Fortunes in the Great War. The Dalmatians inside Austria (ie the majority of Dalmatians) rise up already in February 1914 against the Austrians forming the Free Dalmatian Army (these quickly are incorporated into the command structure of the Army of Dalmatian Hercegovina). This puts a very large chunk of the Austrian Empire into hostile hands very quickly. The Croats (also Austrian subjects) fight so- so loyally until about mid-1916, but then slowly begin to follow the Serb lead and change sides, so that when 1917 rolls around the Croats are already fighting openly against the Austrians.

Austria sues for peace in November 1917, reducing it to its present borders, at least in the south.

The Turks also sign a ceasfire with the Bulgarians, withdrawing to prewar lines.

Montenegro no longer exists, it is once again part of Dalmatia as it was before the Turk entered Europe. Montenegro was basically an artificial state created to give an Austrian ally south of Dalmatian Hercegovina.

The Kingdom of Dalmatia is re-established in February 1918, fusing the Kingdom of Dalmatian Hercegovina together with the Dalmatian lands liberated from Austria.

Oltenia and Moldova are established as independent states in April and May 1918 respectively. After the Ukraine secedes from Russia, Moldova seizes the opportunity to take Odesa from the Ukraine.

Out of Austria, in addition to Dalmatia, three new countries form: The Principality of Slovenia (March 1918), the Banate of Croatia (December 1917) and the Kingdom of Serbia (December 1917). Serbia and Croatia fight a brief battle which leads to Serbia acquiring lands as far as Brcko.

Croatia and Slovenia form a union called the Slavonic Union, in October 1918, in which both are more or less equal partners. Serbia, after some convincing, joins the Slavonic Union in December 1918. With Turkey still a threat in the south and the proposition of a confederation based on the principle of equality of nations appealing, Bulgaria joins the Slavonic Union in January of 1919. Dalmatia is persuaded to join the Slavonic Union too (we're stronger if we're all together, but if you don't join we'll attack you). Dalmatia realises that they are numerous enough to be a loud voice in the Union, so they formally join on 27 March 1919. That same day the Slavonic Union is renamed the Danubian Confederation.