Downtime, aka Crawling in my Ferro-Fibrous Armor (The Clans, part 2)
With The Inner Sphere having manipulated their code of military honor, started down the path of closing the technological gap, and bought themselves time to rearm and unify against a common threat, The Clans decided the best thing they could do would be to start killing each other again for a little while.
Take that, us!
Clan Wolf was decimated by this infighting more than most others (a sliver of their forces broke off and defected to The Inner Sphere. No sane person in the setting considers them traitors for this.), but they also had a pretty good foothold in The Inner Sphere. They staged a number of Trials of Possession where they would fight units from other Clans. If that unit won, well, good on them they all got to go to Chuck-E-Cheese's after the fight. If that unit lost, then they became part and parcel of Clan Wolf and got the titillating privilege of being the first into the fray whenever the war with The Inner Sphere started back up again (believe it or not, Clanners consider this fate superior to an afternoon at Chuck-E-Cheese's). Surprisingly, quite a few units fell during these 'Harvest Trials,' and just gave up their allegiance to their people in order to bolster the depleted ranks of Clan Wolf and gain the slim chance of actually killing people from The Inner Sphere, that is, if the meatgrinder of Clan military service left them as mechwarriors in another eleven years (it probably wouldn't).
The Great Refusal
Somehow, through rapid technological advancement, numerical superiority, massive industrial bases, intelligence gathering, and a collection of generals with their own mostly resolved dramatic story arcs, The Inner Sphere improbably overcame all the advantages of a much smaller society geared entirely around open, direct warfare and managed to destroy a single Clan with Operation Bulldog and Task Force Serpent.
Under the banner of The Star League Defense Force, Inner Sphere forces destroyed Clan Smoke Jaugar holdings in The Inner Sphere, and destroyed every piece of Clan Smoke Jaguar until they reached their capitol, Huntress, where they then decimated the last of their industrial base. Clan Nova Cat defected to The Inner Sphere during this, though they declined to participate in the fighting. No sane person in the universe considers them traitors for this.
It's cool bro. Our spartan warrior culture really has been more of a Christmas and Easter thing for the past 100 years or so anyway.
It's a testament to the resolve of the entire society that none of The Clans took this particularly seriously; formally betting the entire future of their invasion of The Inner Sphere--their raison d'etre--against a coalition who'd just decimated an entire nation in just under a year. If they lost this 'Great Refusal,' they could never again Invade The Inner Sphere. If they won, they could go to war with The Inner Sphere immediately, saving them eight years of waiting.
Just to reiterate: If they lost to the coalition who just destroyed a civilization, the source of the culture's unity and goal for all time would be lost. If they won, they got to start immediately fighting against a fully-mobilized enemy who has just proven themselves capable of wiping them off of the map.
You Know How That Last Part Ended
Action veered away from The Clans for a while, with low-level warfare springing up where the story demanded The Clans do something rather than being utterly irrelevant. If The Clans had a future from which they could look back upon this time period between The Great Refusal and The Jihad, they would probably call it 'the filler period.'
You know that caveat about sane people I keep bringing up every time Clan forces defect to The Inner Sphere? That's specifically for The Word of Blake. Don't get me wrong, the WoB thinks all of The Clans and their descendants are traitors, but they considered those who defected to The Inner Sphere to be much closer targets.
Y'see, some bad things happened when the religiously-fanatacal techno-priests called The Word of Blake, after hanging around their dad's basement for a decade or so, finally asked the rest of the universe if maybe they'd think about going out to a movie some time or something. The rest of the universe declared that dating was dumb, they were in to girls now anyway. The Word of Blake tried to give the universe a gift to get it to change its mind, but to stretch the metaphor right to the end, that gift was a gun and it went off and after that, The WoB kinda figured it was a wanted man anyway so it started shooting people.
And maybe gassing them and nuking them...a little bit. For UNITY!
This period of one, lone psycho nation lashing out randomly at everything else in the universe was called The Jihad. Communications were shut down. Leaders were killed (not any main characters, godforbid), strategy meetings were bombed. Nuclear and biological weapons were dropped. Factories and spaceports were erased from existence. Single-handedly, one group of pro-technology priests restarted the backslide of technology into the dark ages.
Strict Clan styles of combat saw this as abhorrent. The Inner Sphere which had gone to great lengths to demonstrate to The Clans that war was a dirty unpleasant thing which should never be turned into a sterilized game, no matter how ironic that lesson was in light of a universe founded on a war game about shooting each other to death (I give you the link to TV Tropes' Broken Aesop for no reason whatsoever.) decided that if they were to continuously be righteously indignant about every foe so great it caused them to work together in an uneasy alliance, they'd have to start figuring out how to justify fighting dirty while still looking down on The Word of Blake for fighting dirtier still.
Society based on equitable combat? Foolish. Nuclear weapons? That's just unsporting!
Unseating The Word of Blake from Earth was a massive coalition, which many Clans wished to take part in, not only because of their enmity towards The Word of Blake for their actions, but also because of the mythical place that Earth holds in Clan culture.