[3] After a first failed invasion of Serbia where he lost 40,000 men, Oskar Potiorek, the Austro-Hungarian commander of the Balkanstreitkräfte, launched a new offensive across the River Drina at the western Serbian border; after successfully crossing the river the night of 7—8 September the Austro-Hungarian forces were stopped facing strong Serbian defensive positions.

After being defeated in the Battle of Cer in August 1914, the Austro-Hungarian army retreated over the Drina River back into Bosnia and Syrmia.

Under the pressure of the Allies, Serbia conducted an offensive across the Sava river into the Austro-Hungarian region of Syrmia taking Zemun going as far as 20 miles into enemy territory.

It initially went well but finally bogged down in a bloody four-day fight for a peak of the Jagodnja mountain called Mačkov Kamen, in which both sides suffered horrendous losses in successive frontal attacks and counterattacks.

[1] Field Marshal Putnik ordered its troops to take up the position in the surrounding hills, and the front settled in a month and a half of trench warfare.

This was highly unfavourable to the Serbs, who possessed heavy artillery that was largely obsolete, had short ammunition stocks, limited shell production (having only a single factory producing around 100 shells a day) and also a lack of proper footwear since the vast majority of infantry wore the traditional (though state-issued) opanaks, unlike the Austro-Hungarians who had soak-proof leather boots.