From early August 1914, Russia and France pressured Belgrade to invade Austria-Hungary and divert troops from the Eastern and Western fronts.

Despite Serbia's unpreparedness for even a defensive war, let alone an offensive, the pressure mounted as the three powers grew more tense.

The Grand Duke Nikolai Nikolaievich even wrote a letter to Crown Prince Alexander urging him to attack.

Before the Battle of Cer, Serbian Prime Minister Nikola Pašić attempted to buy more time to prepare for the inevitable offensive his country would be forced into by informing the Russian Empire of his lack of pontoon bridges.

Chief of the Serbian General Staff, Field Marshal Putnik, advised Pašić to stall and promise Serbia would only attack once the troops were rearmed and sufficient bridging material was obtained.

[1] On August 31, Putnik invited all the Serbian generals to plan a limited offensive into Hungarian crown lands.

Putnik viewed the operation as without much risk, as it would be easy for the Serbs to retreat in case of major enemy danger.

Field marshal Stepa Stepanović had been told of the plans since August 31 but had not thought to tell General Vladimir Kondic, commander of the division, about them.

Cetnik units crossed to establish a foothold, but the limited defenders on the shore put up fierce resistance and a bridgehead was only gained after two hours of heavy fighting.

Kondic, at this time depressed and solitary, informed Stepanović that an Austrian attack had caused confusion in the ranks, but the order was restored.

However, Stepanović's anger would not change the fact that the 13th regiment of the Timok I division and two additional battalions had been near-annihilated, and the advance of the 1st Army was now severely compromised.

They rapidly and efficiently crossed the Sava River, but due to the failure of the Timok I division, they advanced much more cautiously than they otherwise would.

On September 8, Oskar Potiorek, overall commander of Austro-Hungarian forces in the Balkans, launched an assault on Serbia, deciding it was the best way to stop the Serbian offensive.