Continuously inhabited since the Paleolithic age, the territory of modern-day Serbia, then part of the Roman Empire, experienced Slavic migrations in the 6th century. The first Serb proto-state was established in the 7th century and by the 9th century had developed into a more stable principality, recognized as a tributary state to the Byzantine Empire. The Serbian Kingdom was established in 1217, reaching its territorial apex in 1346 as the Serbian Empire. By the mid-16th century, the Ottoman Empire annexed the entirety of modern-day Serbia; their rule was at times interrupted by the Habsburg Empire, which maintained a foothold in the northern part of the country from the early 18th century. At the beginning of the 19th century, the Serbian Revolution established the Principality of Serbia, which developed into a constitutional monarchy and gained international recognition of its independence in 1878 before being proclaimed a kingdom in 1882. Emerging victorious from World War I, Serbia incorporated the former Habsburg crownland of Vojvodina into its territory in 1918, before uniting that same year with Slovenes and Croats to form the Kingdom of Yugoslavia, ending its existence as a separate political entity. Serbia was re-established after World War II as one of six federal units of socialist Yugoslavia. During the breakup of Yugoslavia, it formed a union with Montenegro, which was dissolved in 2006, subsequently restoring Serbia's independence. In 2008, Kosovo unilaterally declared independence, receiving mixed responses from the international community, while Serbia continues to regard it as part of its sovereign territory.
The battle, part of the first Austro-Hungarian invasion of Serbia, began on the night of 15 August 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 19 August, the morale of the Austro-Hungarians collapsed and thousands of soldiers retreated into Austria-Hungary with many of them drowning in the Drina River as they fled in panic. On 24 August the Serbs re-entered Šabac, marking the end of the battle. (Full article...)