 The Austro @-@ Hungarians entered Valjevo on 15 November , prompting wild public celebrations in Vienna . Franz Joseph praised Potiorek for seizing the town ; cities across the empire made Potiorek an honorary citizen and Sarajevo even named a street after him . Valjevo 's capture led the Austro @-@ Hungarians to believe that they were on the verge of defeating Serbia and that the Serbian Army was no longer a coherent fighting force , but the scorched earth tactics employed by the Serbs during their withdrawal complicated the Austro @-@ Hungarian advance . Although the Austro @-@ Hungarians were right in assuming that the Serbian Army was exhausted , its defensive positions along the Kolubara had been prepared months in advance . Putnik 's carefully timed withdrawals had ensured that the losses of the Serbian Army were lighter than if it had stood and fought pitched battles with the Austro @-@ Hungarians . Moreover , the geography of northwestern Serbia favoured defensive operations since the approaches to the Kolubara did not offer any cover to armies invading from the direction of Austria @-@ Hungary and the river itself was surrounded by mountainous terrain . In October , the Serbs had fortified the Jeljak and Maljen mountain ranges in anticipation of an Austro @-@ Hungarian attack . This gave them an advantage over the Austro @-@ Hungarians as it placed them in control of all roads leading to Kragujevac . The Serbs also established a series of field fortifications blocking the approach to Niš . The extensive series of fortifications and the difficulty of the terrain which they faced left the Austro @-@ Hungarians with no choice but to conduct operations in the gruelling Serbian countryside with almost no lines of communication . 
