Guy and Sibylla were married in 1180; and Guy thus became heir presumptive of the kingdom, if the young Baldwin V., Sibylla's son by her first marriage to William of Montferrat, should die without issue.
Difficulties, however, had arisen with Conrad of Montferrat; and when Guy lost his wife Sibylla in 1190, and Conrad married Isabella, her sister, now heiress of the kingdom, these difficulties culminated in Conrad's laying claim to the crown.
It was only the habit of interurban jealousy which prevented the communes from at once combining to resist demands which threatened their liberty of action, and would leave them passive at the pleasure of a foreign master The diet was opened at Roncaglia near Piacenza, where Fredericli listened to the complaints of Como and Lodi against Milan, of Pavia against Tortona and of the marquis of Montferrat against Asti and Chieri.
Novara, Vercelli, Asti and Tortona swelled its ranks; only Pavia and Montferrat remained imperialist between.
Charles Emmanuel now attempted the acquisition of Montferrat, which was soon to become vacant by the death of Francesco Gonzaga, who held it together with Mantua.