For the next hundred years Ragusa remains under Hungarian protection, but bound by ties so shadowy that for all practical purposes she may be regarded as an independent State. During this period, however, she feels the weight of Turkish power more and more, and her tribute to the Porte goes on increasing, until it reaches the maximum limit of 12,500 ducats. But in spite of this ever-present danger she continues to grow in wealth, splendour, and importance, and to carry out her mission as a haven of refuge and a bulwark of Christianity and civilisation. She flourishes as a centre of learning and the arts no less than as an emporium of trade, and all the while she remains singularly free from internal troubles and constitutional changes—a unique distinction in that part of the world. She pursues the even tenour of her way undisturbed, conservative, aristocratic, narrow-minded, but on the whole successful and prosperous, and her population contented. Very different was the condition of the neighbouring Balkan lands. Bosnia was for the present fairly quiet; the Turks had been driven out of the country, and their leader, Isak Beg, defeated in a raid into Hungary, so that King Tvrtko was able to reoccupy Vrhbosna, and Sandalj Hranić recognised his supremacy for the time being. The long civil war in Croatia and Dalmatia between the partisans of Sigismund and those of Ladislas had resulted in the acquisition of the littoral by Venice, and the only prince who remained independent of the Republic was Ivan Nelipić, Count of Četin, Klissa, and Rama. His estates comprised Western Bosnia and some districts of Hlum and Dalmatia. He could not, of course, face the Venetians on the sea, but he managed to hold his own on the mountain ridges.[364] The Venetians and Tvrtko were ready to come to an understanding on this matter, and a war against Nelipić was under discussion when the Turks again invaded Bosnia. There were 4000 Ottomans in the country all through the summer of 1426, and they seized a number of towns and raided Croatia, Usora, and Srebrnica, while King Tvrtko did not dare to do anything against them.[365] The Ragusan colonies in Novobrdo and Priesrinac were besieged by the Turks and in great danger. The Venetians conducted further operations against them in Albania, the Morea, Achaia, and round Salonica. The routes through Albania, Bosnia, and Slavonia were interrupted,[366] and the inland trade at a standstill.