After being informed of a Serbo-Bulgarian alliance, Venizelos ordered his ambassador in Sofia to prepare a Greco-Bulgarian defense agreement by 14 April 1912, fearing that should Greece fail to participate in a future war against the Ottomans, it would be unable to capture the Greek majority areas of Macedonia. The treaty was signed on 15 July 1912, with the two countries agreeing to assist each other in case of a defensive war and to safeguard the rights of Christian populations in Ottoman held Macedonia, thus joining the loose Balkan League alliance with Serbia, Montenegro and Bulgaria. Fearing a new war in the Balkans, the Ottomans declared mobilization on 14 September and began transferring units to Thrace; the Balkan League responded in kind. On 30 September, the League presented the Ottomans with a list of demands regarding the rights of its Christian population. The Ottoman Empire rebuffed the demands, recalled its ambassadors in Sofia, Belgrade and Athens and expelled the League's negotiators on 4 October, with the latter declaring war against the Ottomans, while Montenegro had already began military operations on 25 September.