Mozart composed some songs that are still sung. This one I don't know. BTW, Chico calls it a 'war song'. If you read it closely, it is not, in spite of the rather warlike first verse. It is, rather, about being emperor - about the power to make war, but also the power to do other things. The mention of Constantinople is hardly surprising as the German emperors (whose line ended only in 1806) saw themselves as the successors of the Roman emperors.