The situation in Italy had begun to deteriorate with the election of a new pope, Formosus, in 891.

Distrustful of Guy, he begins to look elsewhere for support against the emperor, as Guy finds it increasingly difficult to end the threat of Berengar, who still holds out in his Duchy of Friuli.

To bolster his overall position, Guy forces Pope Formosus to crown Lambert as co-emperor at Ravenna on April 30, 892.

The new pope, Formosus, not trusting the newly crowned co-emperors Guy and Lambert, had sent an embassy in 893 to Omuntesberch, where Arnulf was holding a Diet with Svatopluk, to request Arnulf come and liberate Italy, where he would be crowned in Rome.

Arnulf had met the Primores of the Kingdom of Italy, dismissed them with gifts and promised to enter Italy.

In summer 893, Arnulf had sent his son Zwentibold down the Brenner Pass with a Bavarian army to join Berengar of Friuli in Verona.

The two had marched to Guy’s capital, Pavia, and besieged it unsuccessfully, finally renouncing to the siege: according to Liutprand of Cremona, Zwentibold accepted money from Guy in order to leave, although it is not clear if it was in the form of a personal bribe or a tribute to his father.

Zwentibold's retreat is nonetheless seen as a failure, and on hearing the news of the retreat, Arnulf summons a new army and personally leads it across the Alps early in 894.

Bergamo falls in January 894, and Count Ambrose, Guy’s representative in the city, is hung from a tree by the city’s gate.

Arnulf, conquering all of the territory north of the Po, forces the surrender of Milan, then …

…drives Guy out of Pavia, where Arnulf is crowned King of Italy.

Berengar is recognized as king and a vassal of Arnulf.

Zwentibold returns to Germany, as fever has wreaked havoc on the German armies.

Arnulf’s march northward through the Alps is interrupted by Rudolph, King of Transjurane Burgundy, and it is only with great difficulty that Arnulf crosses the mountain range.

In retaliation, Arnulf orders his illegitimate son Zwentibold to ravage Burgundy.

Guy has retreated in order to regroup at a fortified place on the Taro and dies there suddenly on December 12, leaving his son Lambert under the tutelage of his mother Agiltrude, an opponent of the Carolingians.

Both will contest the throne with Berengar and Arnulf.

Ageltrude travels with her fourteen-year-old son to Rome to receive papal confirmation of Arnulf's imperial succession, while her husband marches north with his troops, but Formosus, who still desires to crown Arnulf, is imprisoned in Castel Sant'Angelo.

Guy IV of Spoleto had been granted the Duchies of Spoleto and Camerino in either 888, when his father, Guy II, was crowned King of France, or 889, when his father was crowned King of Italy.

Though his father never secured the French kingdom, he did maintain his Italian crown and thus happily divested himself of his responsibilities in Spoleto itself, the hereditary possession of his family.

A capable warrior and leader, Guy conquers Benevento from the Greeks and makes himself prince here in 895.

He offers the regency of his conquered principality to Guaimar I of Salerno, the husband of his sister Itta, but …

…Guaimar, together with his wife, is captured en route to Benevento by Adelfer, the gastald of Avellino, who he had tried to assassinate.

Guy has to go down and besiege Avellino to get his release.

Guaimar returns to Salerno in disgrace.

A new embassy had arrived in Regensburg in September 895, beseeching Arnulf's aid, and in October Arnulf undertakes his second campaign into Italy.

He crosses the Alps quickly and takes Pavia, then continues slowly, garnering support among the nobility of Tuscany.

First Maginulf, Count of Milan, and then Walfred, Count of Pavia, joins him.

Eventually, even the Margrave Adalbert II abandons Lambert.