864 - The pope sent a message

Norwegian viking church
Denmark
The Pope Nicholas I sent Horik 2. a personal message where he suggested to the danish king that he should abolish his heathen faith and become a christian. But the message was ignored and had no effect.
France
On the 25th of July Charles the Bald funded resources to defense against viking raids when he issued the Edict of Pistres.
a large force of cavalry which was the beginning of the French chivalry. Robert the Strong, margrave of Neustria, attacked the Loire Vikings in a successful campaign. Viking raiders plundered the cities of Limoges and Clermont in Aquitaine.
Pepin II joined the Vikings in an attack on Toulouse. He was captured while besieging the town. Pepin was deposed as king of Aquitaine and imprisoned in Senlis.

Ireland 
The Fragmentary Annals of Ireland report that Irish men of Leinster and Vikings raided Osraige in revenge for Cerball mac Dunlainge's raid, 2 years ago and that Eóganachta of Munster took advantage of this to attack him, so that Cerball raided both his rivals.
Conchobar mac Donnchada, (called the other king of Mide) an ally of Flann against Lorcán, was captured and drowned near Clonard on Amlaibhs order.
Viking Jewel

Tabaristan
The first raid of the Rus raiders occurred during the reign of Hasan ibn Zaid, emir of Tabaristan between 864 and 884. The Rus' sailed to the Caspian Sea and unsuccessfully raided the eastern shore at Abaskun.