Original: The Invasion was a professional wrestling storyline in the World Wrestling Federation (WWF) that began shortly after the WWF's purchase of World Championship Wrestling (WCW).
Simplified: The Invasion was a wrestling storyline in the World Wrestling Federation (WWF) that began after the WWF bought World Championship Wrestling (WCW). During the Monday Night Wars, the World Wrestling Federation (WWF) and World Championship Wrestling (WCW), the top 2 North American wrestling shows, competed for ratings.