Decades of internal political strife had followed the end of the Exarchate of Ravenna in 751 among various settlements vying for supremacy and between pro- and anti-Constantinopolitan factions; attempts by church authorities to acquire temporal influence have also been a factor.

A temporary shift of Venetian loyalties toward the Franks has resulted in somewhat permanent naval conflict in the Adriatic, only interrupted by a truce in 807–808.

The pro-Frankish faction had finally been able to seize power under Obelerio degli Antoneri in 804.

Obelerio and his brother Beato have brought Venice into the orbit of the Carolingian Empire.

However, by calling in Charles's son Pepin, rex Langobardorum, to his defense, Obelerio raises the ire of the populace against himself and his family and they are forced to flee during Pepin's siege of Venice.

The siege proves a costly Carolingian failure.

It lasts six months, with Pepin's army ravaged by the diseases of the local swamps and eventually forced to withdraw.

A few months later Pepin himself will die, apparently as a result of a disease contracted here.

Agnello Participazio had taken up the defense of Venice during the subsequent siege of Pepin of Italy in 810 after the city’s reigning doges, Obelerio, Beato, and Valentino, had called in Pepin to support their tottering power.

Following the flight of Pepin and exile of the doges, Agnello is elected to the dogeship in 811.

Giustiniano had recalled his brother Giovanni from Constantinople, because he has no sons by his wife, and has appointed him to continue the construction of the new church for Venice's new patron saint.

Giovanni succeeds the aged Giustiniano, by election of the assembly, on the latter's death in 829.

The rest of his reign will be occupied by quarrels and problems, internal and external.

The first problem is the return of Obelerio degli Antenori, Doge of Venice from 804 to 811, from Constantinople after twenty years of exile.

He disembarks at Vigilia, near Malamocco, with a band of followers and lays claim to the dogeship.

Malamocco and Vigilia declare for him and both are burned by Giovanni.

Obelerio is killed and his head displayed to the people.

As the community continues to develop and as imperial power wanes, an increasingly anti-Eastern character will emerge, leading to the growth of autonomy and eventual independence.