The Khazar royalty and nobility had converted to Judaism at some point in the last decades of the eighth century or the early ninth century, and part of the general population had followed; to what extent is debated.

Concerning the Khazars, Christian of Stavelot writes in Expositio in Matthaeum Evangelistam 9864), “...in the lands of Gog and Magog who are a Hunnish race and call themselves Gazari there is one tribe, a very belligerent one—Alexander enclosed them and they escaped—and all of them profess the Jewish faith in its entirety.” Some researchers have suggested part of the reason for this mass conversion was political expediency to maintain a degree of neutrality: the Khazar empire is between growing populations, Muslims to the east and Christians to the west.

Both religions recognize Judaism as a forebear and worthy of some respect.

The exact date of the conversion is hotly contested.

It may have occurred as early as 740 or as late as the mid 800s.

Recently discovered numismatic evidence suggests that Judaism was the established state religion by around 830, and though St. Cyril (who visited Khazaria in 861) did not identify the Khazars as Jews, the khagan of that period, Zachariah, had a biblical Hebrew name.

Devín Castle, a Slavic castle founded in the eighth century, has played a crucial role during frequent wars between Great Moravia and the Franks.

The claims that Devín or neighboring Bratislava was the center of Samo's Empire cannot be proven.

The ancient name of the castle (Dowina, from the Slavic/Slovak word deva for girl) is mentioned for the first time in written resources in 864, when Louis the German successfully besieges Prince Rastislav in the "castle of Dowina".

Louis forces Rastislav to acknowledge the supremacy of Eastern Frankish Realm over his kingdom.

Louis is forced in 864 to grant Carloman the kingdom of Bavaria, which he himself had once held under his father.

The removal of the eastern threat and the rise of the Empire’s confidence also opens up opportunities in the west, where the Bulgarian ruler Boris has been negotiating with the Pope and Louis the German for a possible conversion of himself and his pagan people to Christianity.

This expansion of Rome's ecclesiastic influence up to Constantinople's very doorstep cannot be tolerated by the imperial government.

The victorious eastern armies are in 864 transferred to Europe and invade Bulgaria, in a demonstration of military might that persuades Boris to accept Constantinople’s missionaries instead.

Boris is baptized, taking the name Michael in honor of the emperor, thus beginning the Christianization of Bulgaria and initiating the nation's absorption into the Greek-influenced, Eastern Orthodox world.

Boris had originally intended to accept Roman Christianity, but an unsuccessful war with the empire forces him to adopt the Orthodox faith of Constantinople in 864.

At night and in secret, a Greek bishop and priests who have been sent to Pliska, the Bulgarian capital, baptize Boris (who at his baptism takes the Christian name Michael), his family, and the nobles who support his policy.

There is serious opposition by both the nobility and the common people to Boris' attempt to enforce mass baptism.

A pagan rebellion breaks out, and Boris retaliates by executing fifty-two boyars, together with their families.

Oppressive policies in Tabaristan, another dependency of Khorasan, result in the people of this province revolting against Tahirid governance and declaring their allegiance to the independent ruler Hasan ibn Zayd in 864.

Charles the Bald succeeds in gaining control of Aquitaine in 864 after his capture of Pepin II.

Lotharingia’s archbishops, who had been deposed by Nicholas for proclaiming Lothair’s marriage to Teutberga invalid, obtain the support of Emperor Louis, who reaches Rome with an army in February 864; but, having been seized with fever, he makes peace with the pope and leaves the city.

Pope Nicholas now forces Lothair to repudiate the adulterous relationship with Waldrada and reinstate his wife.

Other than adding some lands south of the Jura to his realm and mounting a few feeble expeditions against the Norse pirates, Lothair seems to have done little for its government or its defense.

A report that the emperor Louis II is dead leads to peace between father and sons and attempts by Louis the German to gain the imperial crown for Carloman.

These efforts are thwarted by Louis II, who is not in fact dead, and Louis's old adversary, Charles the Bald.

Orso I Participazio, the fourteenth (traditional) and twelfth (historical) Doge of Venice, is elected in 864 immediately after the assassination of his predecessor, Pietro Tradonico, probably by acclamation.

By the end of the year, the assassins are captured, convicted, and executed, probably beheaded.

Orso continues, like Tradonico, to fight the pirates, Slavic or Saracen, that ply the Adriatic coast, aided by a newly constructed fleet of larger ships.