Below is the source for the above stuff:
In early to mid-2002, WWE underwent a process they called the "Brand Extension". WWE divided itself into two "de facto" wrestling promotions with separate rosters, storylines and authority figures. Raw and SmackDown! would host each division, give its name to the division and essentially compete against each other. The split was a result of WWF purchasing their two biggest competitors, WCW and ECW. The brand extension was publicly announced during a telecast of WWF Raw on March 25, 2002, and became official the next day.
Smackdown has become very famous as it has its own roster. WWE now is the numero uno largest Wrestling organization. Monday Night RAW and Friday Night SMACKDOWN are the two biggies which are really a result of the visionary Vince Mc Mahon.