The Invasion was a professional wrestling storyline in the World Wrestling Federation (WWF, now known as WWE) during the Attitude Era that ran from March to November 2001 and involved stables of wrestlers purporting to represent World Championship Wrestling (WCW) and Extreme Championship Wrestling (ECW)—which merged to form The Alliance—placed against a stable of wrestlers purporting to represent the WWF. The storyline began shortly after the WWF's acquisition of WCW in March 2001, and concluded with a "winner takes all" match between The Alliance and the WWF at Survivor Series.

The idea of a supercard featuring the two top promotions of the Monday Night War was considered to be a dream match scenario in the eyes of many wrestling fans, as it would allow the fans to see which promotion would be superior in kayfabe. The angle began when Mr. McMahon's son, Shane McMahon, announced as part of the storyline on WWF's Raw Is War and the final episode of WCW's Nitro (which merged into a simulcast) that he had bought WCW from under his father's nose. This led to several run-in appearances of WCW wrestlers during Raw Is War and SmackDown! over the months following WrestleMania X-Seven.

In June 2001, the angle grew in intensity as other WWF storylines somewhat abated to make room for the central Invasion storyline. WCW and ECW merged to form The Alliance and challenged the WWF's control over the wrestling industry. An "Inaugural Brawl" took place at the Invasion pay-per-view, where WWF's top star Stone Cold Steve Austin defected and joined The Alliance. Many inter-promotional matches occurred during the Invasion between The Alliance and the WWF, leading up to the climax of the angle at Survivor Series, when Team WWF (The Rock, Chris Jericho, Big Show, The Undertaker and Kane) defeated Team Alliance (Stone Cold Steve Austin, Kurt Angle, Rob Van Dam, Booker T and Shane McMahon) in a "winner take all" elimination tag team match. Immediately after the match, The Alliance disbanded.

The angle saw financial success for the WWF, with the Invasion pay-per-view garnering a buyrate of 775,000, one of the largest non-WrestleMania buyrates in company history. Despite its commercial success, the angle received mixed reviews following its conclusion, and is generally historically considered a major disappointment by fans and critics.

History End of the Monday Night War

During the Monday Night War, the World Wrestling Federation (WWF) and World Championship Wrestling (WCW), the two largest North American wrestling promotions, competed for television ratings. Due to similar developments such as the creations of the New World Order (nWo) and D-Generation X (DX), fans continually compared the two promotions.

Among other factors, mismanagement within WCW eventually led the company to a decrease in popularity, from which it never recovered. The Monday Night War came to an end on March 23, 2001, when the WWF bought the rights to WCW's video library, trademarks, contracts for selected wrestlers, championship belts, and other select properties for what was considered by CNN Money to be a "low bargain price".

The final night of the televised Monday Night War occurred on March 26: Raw Is War primarily focused on the major storylines heading into WWF's WrestleMania X-Seven event, while WCW's Nitro held their final episode with a "Night of Champions" special. Mr. McMahon, the storyline and real-life owner of the WWF, opened up Nitro and announced a simulcast later that night to address the future of WCW. Throughout Raw Is War, McMahon publicly named several WCW wrestlers who would not be retained. Though this was for storyline purposes and most would wrestle for WWF/WWE in the ensuing years, he did legitimately fire Jeff Jarrett on television due to animosity between the two dating back to 1999, when Jarrett blackmailed McMahon for payment after he was booked for a match at No Mercy following his contract expiry the day before. After Sting defeated Ric Flair in WCW's final match, the simulcast began. McMahon talked about the buyout of WCW and toyed with the idea of making WCW into a huge media conglomerate, much like the WWF. He asked the crowd who he should keep under his belt by mentioning names of WCW wrestlers and asking for a reaction. Lex Luger and Hulk Hogan received a negative reaction from fans, and Buff Bagwell, Booker T, Scott Steiner, Sting, and Goldberg received positive reactions. McMahon then proceeded to fire them all, however, to the cheers of the Raw Is War crowd and the jeers of the Nitro crowd. McMahon then announced that he would sign the contract and make the purchase official at WrestleMania, on the condition that Ted Turner would bring the contract for McMahon to sign personally. Shane McMahon, however, appeared on Nitro and announced in kayfabe that he had signed the contract and purchased WCW out from under his father's nose, planting the seed for what was considered a lucrative future storyline opportunity. The Invasion did not begin immediately afterwards, as the WWF was preparing for WrestleMania, the year's largest show, occurring only days after the final night of the Monday Night War.

WCW's first strike; Start of The Invasion

The WWF had effectively doubled the size of its roster through its acquisition of WCW, and as a result, the company believed that there was not enough screen time for many of the new roster members. To alleviate these concerns, the original plan was to find a time slot on TNN (later renamed to Spike TV, now known as Paramount Network) to continue running WCW as a separate entity, with WWF controlling SmackDown! on UPN and WCW controlling Raw Is War on TNN. These plans fell through when no television networks would touch WCW because of its reputation for losing money. The WWF scrapped these plans, however they would eventually carry the idea again in the future for what would later become the brand extension, running two separate brands, with both of the WWF's two existing televised shows, SmackDown! and Raw.

On the May 28 episode of Raw Is War, Lance Storm became the first WCW wrestler to appear on WWF programming, by performing a run-in during a match featuring WWF wrestlers. WCW's Hugh Morrus made his WWF debut on the June 4 episode of Raw Is War by attacking Edge. At King of the Ring on June 24, then-WCW Champion Booker T interfered during the triple threat main event match for the WWF Championship and almost cost Stone Cold Steve Austin the title. Additionally, Austin legitimately suffered fractured bones in his hand from the side slam he took from Booker T into an announce table. The next night on Raw Is War, which was held in New York City's Madison Square Garden, widely considered the WWF's home arena, a confrontation occurred between WCW owner Shane McMahon and WWF owner Mr. McMahon. While Mr. McMahon was in the ring, Booker T came from behind to perform his finishing move, a scissor kick, on him. The WWF roster ran to the ring to aid Mr. McMahon, but Booker T and Shane McMahon escaped through the crowd. This incident marked the official start of the Invasion storyline; Raw Is War commentator Jim Ross announced, "The battle lines have been drawn!" WCW Tag Team Champions Chuck Palumbo and Sean O'Haire then made their WWF debuts on June 28, by invading SmackDown! and attacking the Hardy Boyz and Dudley Boyz during a tag team match, before fleeing after WWF wrestlers came after them in the ring. As they were exiting the arena, they were attacked from behind by other WWF wrestlers led by Hardcore Holly and the APA, preventing what happened with the previous WCW wrestlers running to the arena exits undisturbed and rushing them back into the ring, where they were beaten up by WWF wrestlers.

In July, the WWF tested the idea of a brand extension between WWF and WCW by branding the final twenty minutes of the July 2 episode of Raw Is War under the "WCW" name, with Scott Hudson and Arn Anderson as the announcers in place of Jim Ross and Paul Heyman. During a match between Buff Bagwell and Booker T for the WCW Championship, WWF wrestlers Kurt Angle and then WWF Champion Stone Cold Steve Austin interfered in retaliation by beating Booker T up, with Bagwell joining Angle and Austin in attacking Booker T. This match was poorly received by the audience in attendance at the Tacoma Dome in Tacoma, Washington; sports journalist Michael Landsberg reported that many have called the bout "the worst match ever". One source cited that the match should have showcased the best of WCW, but instead featured too many restholds and not enough action. The audience jeered the wrestlers with chants of "This match sucks!" and "Boring!" A WWF source close to Vince McMahon said that he "absolutely hated" the segment. In a podcast interview with Stone Cold Steve Austin in 2015, Bagwell expressed his suspicions of the WWF's true plans for the WCW product, stating his confusion as to why his match with Booker T took place in Tacoma, Washington (very much a pro-WWF area) instead of on the following week's Raw Is War show at the Philips Arena in Atlanta (the former headquarters city of WCW), where the match likely would have received a more positive fan reception.

Up until this point, the WCW contingent were being depicted as malcontent faces rising up against the heel Mr. McMahon, because of McMahon's bluster during the final Nitro broadcast and Shane's usurping of the WCW ownership. Originally, WCW talents were meant to attack strictly heel WWF wrestlers. The strongly negative reaction of the core WWF viewership to the WCW product and talent, however, coupled with the reality that a WCW wrestling program tailored to appeal to WWF fans would not come to fruition, led to the entire WCW contingent being abruptly turned heel. One example was the heel gimmick of WCW wrestler Diamond Dallas Page, whose first WWF appearance was built up over several weeks in a storyline in which he was portrayed as an anonymous stalker sending invasive videotapes to then-babyface, The Undertaker and his wife.

Addition of ECW; Formation of The Alliance

On the July 9 episode of Raw Is War at Philips Arena in Atlanta, Georgia, Kane was scheduled to face WCW's Mike Awesome and Lance Storm in a handicap match. Chris Jericho came out and offered to be Kane's partner, thus turning it into a tag team match. Near the end of the match, Jericho applied the Walls of Jericho on Storm. As the move was being applied, however, Rob Van Dam and Tommy Dreamer ran through the audience and into the ring and started to beat on Kane and Jericho. In response, WWF wrestlers consisting of The Dudley Boyz, Tazz, Justin Credible, Rhyno, and Raven (all former Extreme Championship Wrestling (ECW) wrestlers) ran to the ring. After a brief stand-off, the WWF cavalry turned around and attacked Kane and Jericho. This prompted Paul Heyman to leave the announce table and enter the ring. After high-fiving the wrestlers, he announced that ECW was entering into the Invasion. Heyman talked about how tired he was sitting beside Jim Ross and discussing WCW versus WWF, stating that he felt that everyone had forgotten about ECW and announced, "This Invasion just got taken to the extreme!".

Later during the night, Shane and Mr. McMahon bumped into each other backstage. Shane told his father that ECW needed to be taken care of and pointed out that there were ten ECW wrestlers under Heyman's belt. He suggested that WWF and WCW field five wrestlers each to take out ECW; Mr. McMahon agreed, but he stubbornly insisted that WCW would eventually meet its demise when all was said and done.