 Complete the following phrase:  With knowledge that Romania was about to join the Allied side, General Sarrail began preparations for an attack on the Bulgarian armies facing his forces. The Germans made plans of their own for a spoiling attack. The German offensive was launched on 17 August, just three days before the French offensive was scheduled to start. In reality, this was a Bulgarian offensive, as the Austro-Hungarian Army was in Albania and only one German division was on the Greek border. The Bulgarians attacked on two fronts. In the east, they easily conquered all Greek territory east of the river Struma see Struma Offensive, since the Greek Army was ordered not to resist by the pro-German King Constantine. In the west, the attack achieved early success thanks to surprise but the Allied forces held a defensive line after two weeks. Having halted the Bulgarian offensive, the Allies staged a counter-attack starting on 12 September 