Guns carried by soldiers into battle have much different requirements than firearms used by civilians for hunting or target practice. An infantry soldier needs a lightweight, accurate, rapid-fire weapon with stopping power, or the ability to render a target immediately harmless. Ideally, a soldier's gun would also exhibit extreme ruggedness and reliability in battle.
Over the years, weapons manufacturers have refined their products to better meet the unique demands of infantry combat. The assault rifle stands as the perfect example. During World War II, military leaders clamored for a weapon that could give their soldiers superior firepower in assault situations. Germany cracked the nut first when it introduced the Sturmgewehr 44 (StG 44) rifle in 1943. The StG 44 came with a 30-round detachable box magazine and could operate in full automatic mode, meaning it fired bullets as long as its trigger was squeezed. It was the first true assault rifle -- and it spawned a number of similar designs, most notably the M16 in the United States and the AK-47 in Russia.
All of these weapons were made for soldiers battling other soldiers. But a funny thing happened on the way to the armistice: Hunters and gun enthusiasts saw the appeal of having a weapon with certain warlike features. As a result, gun manufacturers started making civilian versions of their military firearms. The modern AR-15 rifle, for example, evolved directly from the M16 assault rifle. It doesn't offer full automatic fire, but it otherwise looks and acts like its combat cousin.
Other guns have a similar military lineage. This heritage is a defining characteristic of assault weapons.