text: Area of use In the Middle Ages, on the territory of medieval Croatia formed three dialects; Chakavian, Western Shtokavian and Kajkavian. Initially, the Chakavian dialect covered a much wider area than today: the major part of western-central and southern Croatia southwards of Kupa and westwards of Una river, bordering with the western and southwestern Bosnia and Herzegovina, including all the Eastern Adriatic islands northwest of Mljet, while substratum of Chakavian in Dalmatia possibly existed all the way to Dubrovnik. Croatian dialectologist Petar Šimunović considered that all area until and with Dubrovnik was originally Chakavian. The Dubrovnik area has phonology closer to Southern Chakavian than Eastern Shtokavian. It is possible that some Chakavian idioms were also present in early medieval Montenegro and Albania. However, linguists also point to the fact that it is not possible to draw historical border between Chakavian and Shtokavian, especially Western Shtokavian, with certainty. According to Serbian linguist Pavle Ivić, "the question of where the border of these two dialects was in the Middle Ages is not quite appropriate".
  During and after the Ottoman invasion and subsequent warfare (15th–19th centuries) on the territory of Croatia, the Chakavian dialect area ("jazik hrvatski") became significantly reduced, and on the Croatian mainland, it has been almost completely replaced by the adjacent Shtokavian dialect. In the process the evident dialect continuum was broken as old transitional dialects were lost. Based on 35 letters by Ottoman officers in their native language between the mid-16th and mid-17th century in Dalmatia, almost all of them were Chakavian-Schakavian ikavian. Today, only Northern Chakavian and partly Buzet dialect are widely spoken in the areas where they are located, as all other Chakavian dialects have greatly lost territory, or were assimilated into Shtokavian.