The Kingdom of Illyria was formed to counter the territorial pretenses of the Kingdom of Hungary and the influences of the Russian Empire, but with the Hungarian annexation of the Civilian Croatia and Rijeka lost on its significance.
The legal and administrative reforms made by the former French authorities deeply transformed the administrative structures of these territories, so the Austrian Imperial authorities thought it better to group most of them as a separate administrative entity, enabling a slow incorporation into the Austrian legal, judicial and administrative system.

The Kingdom of Illyria was officially established on 3 August 1816.
In the first years, it also included Croatian territory that was part of Napoleonic Croatie civile.
Already in the early 1820s, however, the pre-Napoleonic Croatian kingdom was re-established, in which also the territories forming part of the Kingdom of Illyria were included (the city of Rijeka-Fiume with eastern Istria and the province of Karlovac).

In the Spring of Nations in 1848, Slovenes advanced a proposal to include Lower Styria in the Kingdom of Illyria, so most of the Slovene Lands would be united in a single administrative entity and the idea of a United Slovenia would thus be achieved.
Peter Kozler designed a map of such an enlarged Kingdom of Illyria, which would later become an important national symbol in the Slovenian national consciousness.
The proposal was, however, rejected by the Habsburg Emperor.
The Kingdom of Illyria was gradually mentioned less and less and for the last time officially appeared in 1849 as a crown land in the March Constitution of Austria.
The Kingdom of Illyria was formed to counter the territorial pretenses of the Kingdom of Hungary and the influences of the Russian Empire, but with the Hungarian annexation of the Civilian Croatia and Rijeka lost on its significance. The legal and administrative reforms made by the former French authorities deeply transformed the administrative structures of these territories, so the Austrian Imperial authorities thought it better to group most of them as a separate administrative entity, enabling a slow incorporation into the Austrian legal, judicial and administrative system.
The Kingdom of Illyria was officially established on 3 August 1816. In the first years, it also included Croatian territory that was part of Napoleonic Croatie civile. Already in the early 1820s, however, the pre-Napoleonic Croatian kingdom was re-established, in which also the territories forming part of the Kingdom of Illyria were included (the city of Rijeka-Fiume with eastern Istria and the province of Karlovac). 
In the Spring of Nations in 1848, Slovenes advanced a proposal to include Lower Styria in the Kingdom of Illyria, so most of the Slovene Lands would be united in a single administrative entity and the idea of a United Slovenia would thus be achieved. Peter Kozler designed a map of such an enlarged Kingdom of Illyria, which would later become an important national symbol in the Slovenian national consciousness. The proposal was, however, rejected by the Habsburg Emperor. The Kingdom of Illyria was gradually mentioned less and less and for the last time officially appeared in 1849 as a crown land in the March Constitution of Austria.
Kingdom of Illyria