FN began developing the P90 in the late 1980s, actually preceding the NATO requirement that it would eventually compete for. The idea of the P90 was to develop a weapon for secondary troops to replace 9mm pistols and SMGs. There was an anticipated threat of Russian paratroops wearing armor that could defeat 9mm ball. The P90 was intended to be a light and handy weapon that was easily controllable without a tremendous about of training, and could defeat that sort of body armor.
The result was the 5.7x28mm cartridge, firing a 31 grain armor-piercing bullet at 2350 fps. This was combined with a simple blowback action and a Hall-style 50-round magazine in a fully ambidextrous, bullpup layout. The gun was introduced onto the market in 1990, and has been widely purchased by security and special operations organizations. In its original intended role for support troops, it has only been adopted by Belgium.