Royal Bulgarian Army reconnaissance car (built in Germany) with an air-cooled gasoline engine in 1940. While the Bulgarians didn’t declare war on Russia, that did not stop the Russians from destroying their country in World War Two.
After Nazi Germany declared war on the United States, three very small countries allied with the Germans, Romania, Hungary, and Bulgaria, followed Hitler’s lead and did the same. President Roosevelt instructed American diplomats resident in those three countries to try and get the declarations of war withdrawn. They did not meet with success and the US declared war on all three of them.
The Germans faced numerous problems with these various armies. They had to provide additional equipment to them and the German Army High Command could never place Romanian units next to Hungarian units because the two countries hated each other and their soldiers would open fire on one another.