Similarly, in North Macedonia, the tension between Serbia and Bulgaria due to the latter's aspirations over Vardar Macedonia generated many incidents between their respective armies, prompting Serbia to keep its army mobilized. Serbia and Greece proposed that each of the three countries reduce its army by one fourth, as a first step to facilitate a peaceful solution, but Bulgaria rejected it. Seeing the omens, Greece and Serbia started a series of negotiations and signed a treaty on 1 June(19 May) 1913. With this treaty, a mutual border was agreed between the two countries, together with an agreement for mutual military and diplomatic support in case of a Bulgarian or/and Austro-Hungarian attack. Tsar Nicholas II of Russia, being well informed, tried to stop the upcoming conflict on 8 June, by sending an identical personal message to the Kings of Bulgaria and Serbia, offering to act as arbitrator according to the provisions of the 1912 Serbo-Bulgarian treaty. But Bulgaria, by making the acceptance of Russian arbitration conditional, in effect denied any discussion, causing Russia to repudiate its alliance with Bulgaria (see Russo-Bulgarian military convention signed 31 May 1902).