Bulgaria, which had the land force in the Balkans, declared war on Serbia in October 1915. Britain, France and Italy responded by declaring war on Bulgaria. In alliance with Germany, Austria-Hungary and the Ottomans, Bulgaria won military victories against Serbia and Romania, occupying much of Macedonia (taking Skopje in October), advancing into Greek Macedonia, and taking Dobruja from Romania in September 1916. Thus Serbia was temporarily knocked out of the war, and Turkey was temporarily rescued from collapse. By 1917, Bulgaria fielded more than a quarter of its 4.5 million population in a 1,200,000-strong army, and inflicted heavy losses on Serbia (Kaymakchalan), Great Britain (Doiran), France (Monastir), the Russian Empire (Dobrich) and the Kingdom of Romania (Tutrakan).