May 23rd, 2002... lights first appeared over Paragon City...
Then sometime in November Omega Team sacraficed their lives (at least, they are all PRESUMED dead.. who knows!? <ominous music>
and destroyed the Rikti's main Portal, thus cutting them off from their home world/dimension.
All found in the wonderful little history section on Paragon City, on this site.
I know, because I needed it for my OWN character, who was here during the war.
<Shamelessly points to his sig>
Now... if only I could finish my "tail" ... <sigh>
I'm trying to make a background for a character and I can't find this information.