The Serbo-Bulgarian War was a war between the Kingdom of Serbiaball and Principality of Bulgariaball.
After the treaty of san stefano, Greater Bulgaria was established, as a puppet state of Russian Empireball. This made great powers create a new peace deal which was decided on congress of berlin. Great Powers didn't allow the creation of greater bulgaria, but gave bulgaria autonomy.
in 1885, Bulgaria reunifies with East Romalia. Ottoman Empireball doesn't react, but Serbia does.
Serbia declares war on bulgaria thinking bulgarian army is weak. Bulgaria beats serbia, and manages to occupy Pirotball.
After Austria-Hungaryball got involved, the war was ended with status quo.