A coastal Balkan principality in the Zeta river valley/highlands, ruled successively by the Balšić noble house (from ~1360) and then the Crnojević house, that maintained precarious independence between Venice, Serbia, and the advancing Ottomans through the 15th century — the direct territorial and dynastic precursor of Montenegro.
Crnojević rule ended under sustained Ottoman pressure; the last Crnojević ruler withdrew and the principality was absorbed into Ottoman territory, with the Cetinje-centered remnant reorganized as the Prince-Bishopric of Montenegro (Q3324486, already in canonical) from 1516 onward.
The atlas holds 4 border frames for Zeta (Balšić–Crnojević principality) — the shape you scrub through changes in 1360 · 1444 · 1454 · 1464.
No dedicated English-language monograph on the Balšić/Crnojević Zeta state was found on Open Library; this is the standard scholarly single-volume history of Montenegro and devotes substantial early chapters specifically to medieval Zeta and the Crnojević era (verified on Open Library, OL3913987W) — used as a sourced fallback per the survey rule.