The P90 and its 5.7×28mm ammunition were developed by FN Herstal in response to NATO requests for a replacement for the 9×19mm Parabellum cartridge and associated pistols and submachine guns.[16] NATO called for two types of weapons chambered for a new cartridge—one a shoulder-fired weapon, and the other a handheld weapon.[16] According to NATO, these new weapons, termed personal defense weapons (PDWs), were to provide "personal protection in last-resort situations when the user is directly endangered by the enemy."

Taken from Wikipedia.org