In addition to territory under direct imperial administration, the Ottoman Empire also possessed varying degrees of sovereignty over its many vassal states. Each vassal state's relationship with the empire was unique, but typically involved the payment of tribute, military contribution, or both. Such vassals included the Danubian Principalities of Wallachia and Moldavia, the Crimean Khanate, the Principality of Transylvania, the Republic of Ragusa, various Georgian and Caucasian principalities, and, in the second half of the seventeenth century, the Cossack state of Right-Bank Ukraine and the territory ruled by Imre Thököly, known as Middle Hungary. The Sharifs of Mecca in western Arabia were also subject to the Ottomans, but neither paid tribute nor offered military forces. At times, the empire also received tribute from Venice, Habsburg Austria, Poland-Lithuania, and Russia, which made them vassals of the Ottoman Empire in theory, if not in practice. The empire's territory also included many smaller and often geographically isolated regions where the state's authority was weak, and local groups could exercise significant degrees of autonomy or even de facto independence. Examples include the highlands of Yemen, the area of Mount Lebanon, mountainous regions of the Balkans such as Montenegro, and much of Kurdistan, where pre-Ottoman dynasties continued to rule under Ottoman authority.