Complex sentence: Later he worked in the Serbian Embassy in Athens until the end of the Balkan wars in 1913, and then moved to Ohrid, that was added to Serbia and became its mayor until Bulgarian anexation of the city in 1915.
Split into simpler sentences: Later he worked in the Serbian Embassy in Athens until the end of the Balkan wars in 1913. Then he moved to Ohrid, that was added to Serbia and became its mayor until Bulgarian anexation of the city in 1915.