When Bulgaria invaded southern Serbia during World War I, it regarded all who celebrated the "slava" as Serbs and enemies, as Bulgarians do not have the custom. For instance, when Bulgarian commander Protogerov was ordered to inflict reprisals in the east of Kumanovo for an earlier attack, and the population quickly declared as Bulgarians before the measures were taken (as to avoid punishment), his aides had the idea of asking the people who celebrated the slava; those who did were shot.