On this day in 1914, Battle of Cer started; fought between invading Austro-Hungarian army and defending Serbian forces, it ended 9 days later with a major Serbian victory, marking the first defeat of the Central Powers in WW1
Austria-Hungary expected a quick victory over Serbia in WW1, having both numerical and technological superiority. On the other hand, Serbian army was still recovering from two brutal Balkan Wars, which happened only a few years prior.
Austro-Hungarian invasion was commanded by General Oskar Potiorek, the Governor of Bosnia and Herzegovina. Before the battle, Potiorek had predicted an easy victory over the Serbians, calling them "pig farmers." The Serbian army was commanded by Crown Prince Alexander and Field Marshal Radomir Putnik as his deputy and de facto military leader. Generals Petar Bojović, Stepa Stepanović and Pavle Jurišić Šturm commanded the 1st, 2nd and 3rd Serbian Armies, respectively.
The battle began on the night of August 15 when elements of the Serbian 1st Combined Division encountered Austro-Hungarian outposts that had been established on the slopes of Cer Mountain earlier in the invasion. The clashes that followed escalated into a battle for control over several towns and villages near the mountain, especially Šabac.
On August 19, the morale of the Austro-Hungarians collapsed and thousands of soldiers retreated back into Austria-Hungary, many of whom drowned in the Drina River as they fled in panic.
After the battle, Austro-Hungarian soldier and journalist Egon Erwin Kisch wrote in his diary about those dramatic moments: "The army has been utterly defeated and is in a ruthless, wild, and panicked flight. A defeated army - no, a shattered mob - was rushing in blind fear towards the border..."