June 28, 1914, Archduke Ferdinand was killed in a tragic assassination. Weeks later, Austria-Hungary demanded the vassalization of Serbia lest they invade the country to enact justice themselves. Peter I refused these demands, and the Central Powers invaded the small Balkan nation. The Entente answered Serbia's pleads for help. The Great War began.
Weeks later, Serbian пробоја поделе (or, without google translate, breakthrough divisions) smashed through the Central Power lines, divisions pouring into the breach past the trenches and overruning the defending forces, pushing from the once besieged city of Belgarde into Bohemia in a week of lighting fast fighting. Days later, the Austrian-Hungarians capitulated to Serbia as Croatian revolutionaries rose up to reclaim their lands from their oppressors in Vienna. The Ottoman Empire and Bulgarians joined the war to enact revenge on Serbia, who had humiliated both in three day wars prior to the Great War. Reserve divisions likewise stormed the trenches of the southern threats, and capitulation soon followed with Russian support in the Middle East.
The German Empire soon went out not with a bang, but a murmur as Serbian and Belgian forces marched into Munich, Berlin and Danzig without opposition, forcing an unconditional surrender on the Central Powers. The final casualties of the Great War were hundreds of thousands among the Central Powers, with the Austrians taking the worst of it at nearly 500,000 dead. The Entente lost a mere ten thousand between them all, most of them Russian.
From the peace conference rose a newly formed Balkan Empire, stretching from the tip of Greece in the south to Danzig in the north. The Serbian army was home before the leaves had even fallen off the trees.
Hearts of Iron 4, the Great War mod