Seeing as I'm the only one here, here's how I would have done the Invasion.
You debut the guys you have as "Former WCW Superstars", but they're NOT in any way affiliated, other than they worked there, now they were here, that's it.
You have have the champions defending their titles as they would normally, the main event of SmackDown is Booker T defending the WCW World Heavyweight Championship vs. fuck it, let's just say Hardcore Holly, the purpose isn't for Holly to become champion, it's for Booker T to look like a bad ass, a guy who is the equivalent to The Rock, Stone Cold etc.
More importantly KEEP THE WCW GUYS STRONG!!
So, we head into Vengeance, and we have all of the WWF and WCW Championships combined as WCW is no longer an entity, there's no need for seperate championships.
Now, we head into the new year, Ric Flair makes his return to the WWF, seemingly attempting to force an alliance between the former WCW guys, everyone knows he's up to something, and he's immediately banned from all WWF arenas, but the WCW guys are starting to get a little territorial and paranoid, and the WWF guys are noticing that they're getting terriorial and paranoid, they start getting territorial and paranoid, and something begins to bubble, and we're heading into the Royal Rumble, and battle lines are being drawn, and at the Royal Rumble, Kevin Nash makes his return, is he WCW? Or is he WWF?
Every guys he saves from elimination seemingly an indication of allegiance, he saves DDP "He must be WCW!" he saves Kurt Angle "He must be WWF" whose side is Nash on? HHH wins the Rumble and goes to WrestleMania, But questions are being asked of Kevin Nash, and those questions aren't being answered, and even more questions are raised when Scott Hall turns up, and they win the Tag Team titles.
We're heading into WrestleMania, Ric Flair finally manages to get into a building, long enough to talk to Chris Jericho, before Vince catches him, and has The APA, drag him down to the ring, with a few other guys, and cuts a promo saying "Since you've turned up, this place has been chaotic, I know you're trying to stage a WCW coup, and I'll kill you before I'll let you even try", and Flair is subjected to a beating, until former WCW guys come to Flair's aide, it's official, the war between the WWF and WCW is on, and it's gonna happen at WrestleMania, in a No Holds Barred Turf War.
WrestleMania finally happens, after weeks of near riots consuming the arena, the WWF comes out on top (of course), but there are casualties of war, as literally nobody is left standing, WrestleMania, has turned into a crime scene, as all the participants are helped out of the arena ready for the main event, as Royal Rumble winner, Triple H takes on Chris Jericho for the World Championship, and during the match, Hall and Nash appear, and help HHH win the World Heavyweight Championship, the Kliq rules professional wrestling once again.
HHH, Hall and Nash appear the next night on Raw, and are immediately confronted by The Rock, the Undertaker and Kane. And a match is made for the main event, where X-Pac interferes, helping HHH, Hall and Nash pick up the win. The foursome are doing everything in their power to keep the world title in their group, interfering in every match, with The Kliq seemingly amassing more members in, helping HHH beat the likes of Rock, Jericho, Undertaker, Kane, Booker T, Steve Austin, one of the men orchestrating everything revealing himself... Hulk Hogan. This isn't the "The Kliq" they're dealing with, it's the nWo!! Ric Flair wasn't trying to take over the WWF, he was assembling the front line to protect it. More questions arise, why would HHH align with the nWo? Why is Vince not stepping in to stop them?
Well, this is where it all falls into place. Flair and Vince are in the ring, Flair asks Vince one simple question, "Did you form the nWo to take down WCW?" and you go for the "A Few Good Men", before Vince says "YOU BET YOUR ASS I DID!!" before going off on a diatribe that "Ted Turner just threw money around, signing Vince McMahon's guys after he made them stars, Hogan, Hall, Nash, Hennig, X-Pac, all my guys! But there's something money can't buy, and that's LOYALTY! Ted Turner paid hundreds on millions of dollars on Vince McMahon's cancer! A cancer that ate WCW from the inside, leaving it a husk of what it was, and when the job was done, they all came home to take what is rightfully their's, THE WORLD!!"
The Alliance wasn't WCW and ECW, it's the WWF, WCW and ECW vs. The nWo!