“The Bulgarian army was a veteran force due to its participation in the Balkan Wars. In the First World War it committed two armies to the campaign that overran Serbia. The victory established a direct connection between the Austro-German and Bulgarian-Ottoman halves of the Central Alliance. The Bulgarian army then held in place 300,000 Entente soldiers who might have been utilized on the Western Front or elsewhere. Without the participation of Bulgaria in its ranks,the Central Powers might not have held out until the autumn of 1918 against the Entente. Surely the German connection to the Ottoman Empire would have remained tenuous, and the Romanian threat to Austria-Hungary could have proved viable. Had the Bulgarians not endured as long as they did on the Macedonian Front, an Entente thrust could have broken through and brought about the collapse of the other Central Powers allies against the more numerous,better-fed, and better-equipped Entente opponents as early as 1916.”
— Hall, Richard, “Bulgaria in the First World War,” Phi Alpha Theta Volume 73, Issue 2 (2011), p. 315.