The Italian government became increasingly aggravated in 1915 with the passive nature of the Serbian army, which had not engaged in a serious offensive against Austria-Hungary for months. The Italian government blamed Serbian military inactiveness for allowing the Austro-Hungarians to muster their armies against Italy. Cadorna suspected that Serbia was attempting to negotiate an end to fighting with Austria-Hungary and addressed this to foreign minister Sidney Sonnino, who himself bitterly claimed that Serbia was an unreliable ally. Relations between Italy and Serbia became so cold that the other Allied nations were forced to abandon the idea of forming a united Balkan front against Austria-Hungary. In negotiations, Sonnino remained prepared to allow Bosnia to join Serbia, but refused to discuss the fate of Dalmazia, which was claimed both by Italy and by Pan-Slavists in Serbia. As Serbia fell to the Austro-Hungarian and German forces in 1915, Cadorna proposed sending 60,000 men to land in Thessaloniki to help the Serbs now in exile in Greece and the Principality of Albania to fight off the opposing forces, but the Italian government's bitterness to Serbia resulted in the proposal being rejected.