Original: It was then a piece for the theater play "Marko kazuje na kome je carstvo" (Marko Names The Emperor), and its immense popularity with audiences prompted its adoption as the Serbian national anthem.
Simplified: Original source was a piece for the theater play "Marko kazuje na kome je carstvo" (Marko Names The Emperor), and it's famous popularity with public wanted Bože Pravde as the Serbian national anthem.