Personal Union of Hungary and Bohemia is a central European state which was a neighbour of the Ottoman Empire and Poland. It was almost constantly in a state war either with the Ottomans or the Protestants. From 1526 to 1563 the borders were questionable, only then did the Ottomans recognized the southern border. It eventually had to give up Ottoman Transylvania to the Ottomans.
Louis II inherited the kingdoms from his father Vladislaus II and not long after Hungary became constantly occupied by Ottomans, because he insulted them despite their large territory, but for time during which he battled, he was always afraid he will die and the kingdoms would split, leaving it open to attack. He therefore decided to speak with lords of Bohemia and lords of Hungary and they all decided that Louis' successor will definitely rule both kingdoms. In 1543 however most lords of Hungary were landless as the Ottomans went straight for the north. Louis II died in battle that same year. Casimir I was crowned in Bohemia and started to free Hungary with the help of his kinsman Sigismund I of Poland (later his son Sigismund II of Poland) and donations of Charles V. The age was one of war from both sides, Casimir even made it to Constantinople, when Suleiman left his son as commander. But this didn't last, because Suleiman send him back a eventually in 1563 Casimir had to give up several places in the south. Finally Suleiman signed peace. Although Ottoman Transylvania was a rather useless land, as it was reoccupied by either sides about six times. The river Tisa was made the border, though Casimir originally wanted Mures river to be the border, however Suleiman wanted a lot more.