The Allied forces in Salonika launched their biggest offensive against Bulgaria in 1918. With the abdication of the pro-German King Constantine of Greece in June 1917, the Greek government had declared war against the Central Powers. With the Russians out of the war, the Allies were in need of this extra manpower.
There was fierce fighting in September 1918 on the border between Greece, Macedonia and Bulgaria. On 18 and 19 September the Allied forces (including a large Welsh contingent) attacked in the mountainous area around Doiran Lake. The Bulgarian forces were able to repel these attacks, but soon afterwards they withdrew from their positions.
By this time the Bulgarian government knew the Germans were struggling on the Western Front and the Austro-Hungarian and Ottoman Empires were crumbling. They believed the war was lost.
The Allied attack captured the city of Skopje. Retreating Bulgarian soldiers mutinied and thousands of them threatened to march on the Bulgarian capital Sofia. On 29th September Bulgaria asked for an armistice.