The war expands a bit more. Bulgaria declared war on Romania. Bulgaria was a German ally in the war.
Unlike Romania, however Bulgaria had been at war since October 1915. War with Romania had not been contemplated by the Central Powers until the summer of 1915 at which time contingency plans for the same were created. By the time of the Bulgarian declaration of war the Central Powers were in fact well prepared for war in the region, a fairly amazing feat given how stretched their resources then were.