The year was 2001. The Monday Night Wars and the Attitude Era were coming to a close. WCW, who had fought tooth and nail with the WWF for years, was collapsing and had become a shadow of its former self. The writing was on the wall, and everyone knew it was only a matter of time before WCW was nothing but a memory. Even then, no one ever expected that one day, Vince McMahon would appear on WCW's Monday Nitro to announce that the WWF had purchased WCW, and that the fate of the company was now in his hands.
At the end of what would be the final broadcast of Nitro, however, Shane McMahon had a surprise for his father. He had swooped in and purchased WCW right out from under Vince's nose. And he vowed that WCW would kick the WWF's ass all over again. This was the opening salvo in what would later be called the Invasion angle (stylized as InVasion).
A couple months later, the invasion began in force as WCW wrestlers began doing run-ins and attacking WWF wrestlers. With wrestlers like Booker T and Diamond Dallas Page at his command, Shane was poised to overthrow his father. And he soon had help, in the form of Paul Heyman's ECW, which was owned by Stephanie McMahon. The two companies had merged to form an alliance (henceforth known as The Alliance) with their sole goal being to end Vince McMahon's WWF.
The InVasion reached its climax at its eponymous pay-per-view, when "Stone Cold" Steve Austin defected from the WWF and joined the Alliance. In retaliation, Vince McMahon had reinstated The Rock, who was previously suspended earlier on in the year after WrestleMania X-Seven. The war between the two factions continued, and the WWF suffered another setback when Kurt Angle also jumped ship and joined the Alliance.
The final battle between the two factions would be at that year's Survivor Series, with five members of Team WWF taking on five members of Team Alliance, with the loser being forced out of wrestling forever. Team WWF would emerge victorious, thanks to Kurt Angle revealing himself as The Mole and backstabbing Team Alliance. With their defeat, the Alliance was dissolved and their threat to WWF had ended.
It sounds like a great story in kayfabe, doesn't it?
Behind the scenes, it was a much different story.
It is true that Vince McMahon had bought out WCW for pennies on the dollar. Unfortunately, a lot of the wrestler contracts were still held by WCW's holding company, AOL-Time Warner. And a lot of those wrestlers elected to "sit out" their contracts, content to be paid for doing nothing, rather than let themselves be bought out by Vince. This left WCW severely lacking in superstar talent. Adding to the trouble were the gimmicks and storylines the former WCW wrestlers were given, including Diamond Dallas Page being booked as a stalker of The Undertaker's then-wife at the time Sara.
On top of that, the Alliance was booked to look weak, with WWF wrestlers winning cleanly and WCW/ECW wrestlers only getting wins in controversial fashion, such as via interference. The dream matches that fans were hoping to see, notably Sting vs. Undertaker never materialized (or only happened well after the Invasion had ended), and the whole thing was seen as just a Vince McMahon ego trip, patting himself on the back for having taken out his competition.
This was made clear at the final battle at Survivor Series, where the only two members of Team Alliance that would be considered WCW or ECW stars were Booker T and Rob Van Dam. They were quickly eliminated from the match, and ultimately the match would come down to The Rock vs. "Stone Cold" Steve Austin, two WWF stalwarts (though Austin did spend some time in both WCW and ECW.)
The entire InVasion angle was inducted into WrestleCrap and won the 2001 Gooker Award. That same year, The Wrestling Observer Newsletter gave the feud between WWF and The Alliance the "Worst Feud of the Year" award.
With the InVasion angle over and any traces of the Attitude Era gone for good, the WWF now had to look for a new presentation going forward. The answer came a few months later: Ruthless Aggression.