The most notable Serbian linguist of the 19th century, Vuk Karadžić, declared that all south Slavs that speak the štokavian dialect (in the central south Slavic language group) are Serbs who speak the Serbian language. This is perceived as one of the steps in paving the way for annexation of territories inhabited by such people, to the dismay of nationalists among the other peoples also living there.
The ideology has been put in action several times during the 19th and 20th century, notably in Serbia's southward expansion in the Balkan Wars, the de facto westward expansion by the forming of the Kingdom of Yugoslavia, and another attempted westward expansion in the breakup of socialist Yugoslavia in the 1990s (partially successful, cf. Republika Srpska).
Critics argue that the concept as such is void, or note lack of continuity in the application of the idea. Despite attempts at denying it, the existence of this idea has often been and continues to be a deterrent of the good relations between Serbians and other neighbouring peoples. Many Croats argue that it has incited the Ustaše movement and all that ensued.