Koča's frontier rebellion (Kočina Krajina revolt) was an uprising of Serbs against the Ottoman Empire from February 1788 - September 7, 1788. Koča Andjelković (b. 1755 - d. 1788) was the leader of the uprising which was aided by the Habsburg Empire. It enabled the Habsburgs to conquer Serbia from the Ottomans, attaching the territory of the Pashaluk of Belgrade to other Serb-populated areas of their Empire. The crownland of (third) Habsburg Serbia existed for 3 years.

By 1791 however the Austrians were forced into withdrawal across the Danube and Sava rivers, joined by thousands of Serbian families who feared Ottoman revenge for supporting the Habsburgs. The uprising also involved the hero of the Serbian revolution Karadjordje Petrovic, who served in the Austrian army at the time. Retaliation of the Ottomans in the outset of the uprising influenced the Serb determination to emancipate from the Ottomans 15 years later, during the Serbian revolution.

A frontier is a political and geographical term referring to areas near or beyond a boundary. It was absorbed into English from French in the 15th century, with the meaning "borderland"—the region of a country that fronts on another country (see also marches).

The word "frontier" also means a region at the edge of a settled area, especially in North American development. It is a transition zone where explorers, pioneers and settlers were arriving. That is, as pioneers moved into the "frontier zone", they were changed by the encounter.

That is what Frederick Jackson Turner called "the significance of the frontier". For example, Turner argued that, in United States' 1893, one change was that unlimited free land in this zone was available, and thus offered the psychological sense of unlimited of opportunity. This, in turn, had many consequences such as optimism, future orientation, shedding of restraints due to land scarcity, and wastefulness of natural resources.

In the earliest days of European settlement of the Atlantic coast, the frontier was essentially any part of the forested interior of the continent lying beyond the fringe of existing settlements along the coast and the great rivers, such as the St. Lawrence, Connecticut, Hudson, Delaware, Susquehanna River and James.