Triune Kingdom (Croatian: Trojedna kraljevina) was a notion advocated by the leaders of the 19th-century Croatian national revival, that for most of the second millennium, there existed three Croatian realms—Croatia, Slavonia, and Dalmatia, which were united only under a single king, yet politically and administratively separated, meaning the term persisted largely in a formal context.
Within the Habsburg Monarchy, before 1848, the Triune Kingdom was advocated by the Croats, but their claims on large parts of the territory were contested within the monarchy both by the Hungarians and by the Vienna Court War Council, and outside the monarchy by the Ottoman Empire. During the Revolutions of 1848, the notion of a triune kingdom that would be the territory of the Croatian cultural and political union was used by proponents of Croatian nationalism. Political representatives of Croatia advocated the notion with the Emperor and demanded the unification of the three kingdoms. Following the Austro-Hungarian Compromise of 1867 and the Croatian-Hungarian Settlement of 1868, the Hungarian claims on Slavonia and Austrian claims on the Military Frontier were formally relinquished, but there was no change in the status of Dalmatia. In the Croatian-Hungarian Settlement of 1868, the territory known as Lands of the Crown of Saint Stephen was officially defined (art. 1) as "a state union of the Kingdom of Hungary and the Kingdoms of Dalmatia, Croatia and Slavonia."
In 1874, Ivan Kukuljević Sakcinski published various archival funds and collections in his work Codex Diplomaticus that is now kept in the Croatian State Archives, demonstrating documents from all periods that speak of the Kingdom of Croatia, Dalmatia and Slavonia consisting of:
- Privileges – Privilegia Regnorum Croatiae, Dalmatiae et Slavoniae, dated 1377
- Protocols – Protocolla Congregatio generalis Regnorum Croatiae, Dalmatiae et Slavoniae, dated 1557
- Minutes – Acta Congregationum Regni, dated 1562
- Minutes – Transumpta documentorum iura Croatica tangentium, dated 1249
The specific term Triune Kingdom of Dalmatia, Croatia, and Slavonia was used for the Medieval Croatian Kingdom, and the first centuries of the Habsburg Kingdom of Croatia, up to the early 19th century. The term Triune Kingdom of Croatia, Slavonia, and Dalmatia was used for both the late period (first half of the 19th century) of the Habsburg Kingdom of Croatia, and its successor the Kingdom of Croatia-Slavonia. The order of mentioning Dalmatia was a contentious issue, as it was ordered differently in the Croatian and Hungarian language versions of the 1868 Settlement.
- Jakić & Balta 2007, p. 273.
- Romsics & Király 1999, p. 177.
- Korunić 1999, pp. 12–13.
- Goldstein & Jovanović 1999, p. 68.
- Goldstein & Jovanović 1999, p. 77.
- Goldstein & Jovanović 1999, pp. 102-103.
- Romsics & Király 1999, p. 194.
- Hugh Seton-Watson, Nations and States. Part 32, 1977, p. 133.
- Kukuljevic-Sakcinski, Ivan von [Hrsg.]. - Zagreb (1874), Codex diplomaticus regni Croatiae, Dalmatiae et Slavoniae 
- Codex diplomaticus regni Croatiae, Dalmatiae et Slavoniae, Volumes 1-2, Tiskom D. Albrechta, 1874, 
- Charles Jelavich, Barbara Jelavich, The Establishment of the Balkan National States, 1804-1920, University of Washington Press, 1977, p. 253
- Romsics & Király 1999, p. 178.
- Barbara Jelavich, History of the Balkans: Twentieth century, 1999 edition, p.57, "The National Party [in Dalmatia] wished to be united with Croatia to form a reconstituted Triune Kingdom."
- Goldstein & Jovanović 1999.
- Sabotič & Matković 2005, p. 168: [...] Zakona o izbornom redu za kraljevinu Dalmacije, Hrvatske i Slavonije
- Mikuláš Teich, Roy Porter, The National Question in Europe in Historical Context, 1993, p.284
- Jakić, Ivana; Balta, Ivan (May 2007). "Pregled zbivanja u predpreporodnom i preporodnom razdoblju do osnivanja političkih stranaka (1841.)". Povijesni zbornik: godišnjak za kulturu i povijesno nasljeđe (in Croatian) (Faculty of Philosophy, University of Osijek) 1 (1-2): 273–284. ISSN 1846-3819. Retrieved 2013-12-31.
- Goldstein, Ivo; Jovanović, Nikolina (1999). Croatia: a history. C. Hurst & Co. Publishers. ISBN 1-85065-525-1.
- Romsics, Ignác; Király, Béla K. (1999). Geopolitics in the Danube Region.
- Korunić, Petar (April 1999). "Hrvatski nacionalni program i društvene promjene za revolucije 1848/49. godine" [National Programme and Social Change during the Revolution in 1848-1849.]. Journal - Institute of Croatian History (Faculty of Philosophy, University of Zagreb) 31 (1): 12–13. ISSN 0353-295X. Retrieved 2012-08-21.
- Sabotič, Ines; Matković, Stjepan (April 2005). "Saborski izbori i zagrebačka izborna tijela na prijelazu iz 19. u 20. stoljeće" [Parliamentary Elections and Zagreb Electoral Bodies at the Turn of the 19th and 20th Centuries]. Društvena istraživanja: Journal for General Social Issues (in Croatian) (Zagreb, Croatia: Institute of Social Sciences Ivo Pilar) 14 (1-2 (75-76)). ISSN 1330-0288. Retrieved 2012-08-22.
- (Croatian) Croatian–Hungarian Settlement