They described the horrors conducted by Margrave Cadolah of Friuli (800-819) and his men in Pannonia, but the King of Franks refused to make peace.

In July 819 on the Council in Ingelheim Ljudevit's emissaries offered truce conditions, but Emperor Louis refused; demanding more concessions to him.

As soon as the winter retreated, massive Frankish armies were being amassed in Italia, East Francia, Bavaria, Saxony and Alemannia that were going to simultaneously invade Ljudevit's lands in the spring.

Ljudevit concluded that all resistance would be futile, so he retreated to a stronghold that he built on top of hill that was heavily fortified; while his people took shelter in local forest and swamps.

The Franks eventually retreated from his lands, with their ranks thinned by disease which the northern forces caught in the marshes of Drava.

The Slavs from Carantania lost their internal independence and were forced to recognize the Friulian margrave Balderic as their ruler, while some remained loyal to Ljudevit.

During the last and final Frankish invasion of 822, the Patriarch from Grado, Fortunat, who was a supporter of Ljudevit, fled to Zadar into exile with the Byzantines.

According to Einhard, the writer of the Royal Frankish Annals, following the final Frankish attack, Ljudevit fled from his seat in Sisak to the Serbs in 822 (Siscia civitate relicta, ad Sorabos, quae natio magnam Dalmatiae partem obtinere dicitur, fugiendo se contulit; "abandoned the city of Siscia and sought refuge among the Serbs, who, as they say [agent of information], rule over a large portion of Dalmatia"[5]).

Tadija Smičiklas did not attempt to define the area where Ljudevit fled, while Vjekoslav Klaić wrote it was beyond Sava and Bosna.

The 1953 "History of the peoples of Yugoslavia" published by Školska knjiga added apparently fictitious details to the original story.

[10] Svetislav M. Prvanović tried to connect Ljudevit and the Guduscani with the Roman city of Guduscum in eastern Serbia, but using only the interpretation of a single comma in Franjo Rački's text and conjecture.

[12] Ivo Goldstein acknowledged and accepted the theory that it was located in Srb, but advocated against misinterpreting the scarce historical records.

[13] Radoslav Katičić argued against the theory, and Tibor Živković concurred with him,[14] concluding such an idea is "misleading" and "not well established", because the source talks about Serbs not Srb, as holding a large part of Dalmatia and not some "small area around the town of Srb" among others, that "much more accurate to understand that Ludovicus escaped from Siscia by the river Sava to the mouth of Vrbas into Sava".

[17] However, opposing to Fine, Tibor Živković says that the second-hand accounts given to the Franks by their agents in Siscia and Croatia establish the existence of some sort of a Serbian claim to rule and have political power over parts of (Roman) Dalmatia, similar to the analogous Frankish claim, but not necessarily settlement outside of places already known from other sources.