The Game starts at an early timepoint in the MechWarrior-Cycle where Clan-Wars were not present.
Clan-War is an option for a later update in futur (NO known timepoint atm).
Isn't the time frame for the Clan Invasion known? The game is an MMO that occurs in real time parralell to earth's time (Jan 2012 == Jan 3049). Since we know this, and we know that the Clan Invasion commenced sometime in late 3049/early 3050 (sarna.net sites it at August 3049) we can deduce that the Clan Invasions should occur within the first year of MWO's launch, but not at launch.