Bulgaria’s entry into World War I had a significant impact on the Ottoman Empire and their war on their multiple fronts.
For one, with Bulgaria joining the Central Powers allowed for a multi-blow assault on Serbia forcing them out of the war. At the end of 1915 there was a continuous supply line from the Western Front in France to the Tigris River Valley.
This allowed for supplies flowing to the Ottomans as well as Ottoman troops being sent west, fighting on the Galician Front.
Figures shown are from my friends at Irregular Miniatures.