Faced with trench warfare, WWI troops needed a portable weapon with enough firepower to change the course of a battle. Leave it to John Browning to come up with a perfect answer: the Browning Automatic Rifle.
Although it entered WWI at the tail end of the conflict, the BAR had a measurable impact on some of the final battles. The French were so impressed, that they ordered 15,000 of them to replace their own maligned Chauchat. The BAR had made its mark in a very short time.
Between WWI and WWII there were many modifications being on worked on for the BAR. From pistol grip versions to bayonet mounts, but when the U.S. entered the second World War, the BAR wasn't very different from Browning's original design.
As you would guess, firearms achieve incredible advances during times of armed conflict. Government and private firms dedicate the best people and technologies to bring about new weapons to help troops be more effective on the battlefield. While these think tanks have provided great achievements in small arms development, they draw from many things accomplished in the past. Modern squad automatic weapons are one of the most important aspects of infantry tactics and firepower, but the original squad weapon, and arguably the most successful to date was developed by one man. A man whose name seems to be found in virtually all lineages of firearms development.