Warmatrix

While the western European powers that would dominate the European Age were slowly gaining strength, in the east two massive superpowers were already established: the Habsburg empire and the Ottoman empire. Inevitably the two imperialist states clashed with each other and over the course of more than 2½ centuries fought several wars. Despite a lot of fighting, their mutual border shifted but little.
After establishing their state in Anatolia in the Late Middle Age, the Ottomans expanded their territory over all of Asia Minor and the southern Balkans. In 1453 CE they took the city of Constantinople and ended the Byzantine empire. Afterwards they started to advance northwest, conquering the rest of the Balkans. Meanwhile the Habsburg family, starting from Austria, increased its power mostly through strategic marriages. Their power grew so great that they could secure the position of emperor of the Holy Roman Empire. When the Ottomans defeated the Hungarians in the (first) Battle of Mohács in 1526 CE, the Habsburg archduke Ferdinand of Austria inherited the throne of Bohemia and Hungary, which brought him in direct conflict with the Ottoman empire.
Ferdinand captured parts of Hungary, including the city of Buda. The Ottoman sultan, Suleiman the Magnificent, was slow to react but in 1529 CE struck back and besieged Vienna itself. However the Turks failed to take the city. The fighting shifted back to Hungary, where the two states battled each other for three decades in the Little War of Hungary. In it, the Turks conquered most of Hungary step by step, leaving the Habsburgs only the northwestern rump. They also forced the Habsburgs to pay an annual tribute.
The might of the Ottoman empire was far greater than that of the Habsburg empire, yet the strategic situation hindered them. The Balkans had little food surplus, so the Ottomans had to bring supplies from their heartland. Because the terrain was wooded and rugged these transports were restricted to rivers, which limited the campaigning season. With numerical inferiority on one side and logistical problems on the other, neither managed to achieve a decisive advantage. Warfare was mostly restricted to raiding and counter-raiding. Most of the Balkan lands remained firmly in Ottoman hands, because they allowed a lot of religious freedom and did not overtax the peasants, so the latter had little incentive to throw off the muslim yoke.
In the meanwhile the Ottoman empire attacked on another front too. Originally a land power, it created a navy and expanded in the eastern Mediterranean. There the main enemy was Spain, then ruled by another branch of the Habsburg empire, with Italian city states like Venice caught between the two giants. The Ottomans attacked Rhodos in 1480 CE; conquered it 1522 CE; took Cyprus in 1570 CE and allied themselves with north African pirates. But they were halted at Malta and Lepanto.
The Habsburgs used the quiet to upgrade their oldfashioned and ineffective border forts, modernize their military and finances, though they were hampered by old traditions that were hard to weed out. In 1592 CE emperor Rudolf felt strong enough and refused to pay further tribute. A year later the Long Turkish War broke out, which lasted until 1606 CE. Again a lot of fighting took place on Hungarian soil. The Ottoman vassals Transsylvania, Wallachia and Moldavia rebelled at various points, giving the Ottoman sultans a lot of headaches. The Habsburgs scored some victories but suffered a few heavy defeats too; the overall balance of power shifted somewhat to the Habsburg side. They got half-allies: Poland fought against the Turks over Moldavia; Transylvania became semi-independent. Finally the Ottomans had to cede western Hungary.
The Turks reacted by enlisting many aquebusiers into their army, but this diluted the quality of the army and strained the treasury. The Ottoman empire was forced to decentralize and many soldiers were tied down in garrison duty, to keep the provinces under control. Inflation, caused by a steady influx of silver from America, further added to the problems. However the decline in power was gradual and in 1663 CE the Ottomans, after several decades of relative peace, still felt strong enough to take the offensive again. They were repulsed at the Battle of Saint Gotthard; made another attempt in 1683 CE, besieging Vienna once more, again without success. This was because on the other side, the Habsburgs had grown in power. By now they were able to raise large armies of their own, armed with the latest European weaponry and tactics. At the second Battle of Mohács in 1687 CE they avenged their earlier defeat and pushed south. In 1699 CE peace was made once again, which cost the Ottomans most of Hungary.
During the 18th century CE the two empires fought several more wars, also involving a new great power: Russia. These were the War of the Spanish Succession; the Austro-Turkish War of 1716 CE - 1718 CE; Austro-Russian-Turkish War of 1735 CE - 1739 CE; the Austro-Turkish War of 1787 CE - 1791 CE. In these, the Habsburg empire was the stronger power. Only conflicts with other European powers kept it from an all-out attack, though it conquered the rest of Hungary, Croatia, Bosnia and Herzegovina.
In the 19th century CE the Habsburg empire became the Austrian empire and later Austro-Hungarian empire. The Ottoman empire suffered several revolts and loss of territory in the Balkans. Both states lacked the heavy industrial power to keep up with western Europe and their power slowly declined. In the 20th century CE both were broken up after World War I.