The biggest strength and greatest failing of the False Emporer's Imperium is that it's armies are so vast that they treat war like a game of chess. wear down the opponent by simply overwhelming him and killing everyone. as long as you win, no one cares how many of your people died in the process.

Were i the Leader of a Black Crusade, I would spend centuries, Milennia even, planning my glorious march and collecting resources. Start by claiming Systems the Imperium doesnt know/care about. between hereteks, Daemonic inspiration, and traitor rogue trader and navigator houses (they're out there) it would be very easy to carve out Warp lanes to star systems that hold riches and knowledge the imperium doesnt have. In this sense, you create a kind of Anti-Imperium (or true Imperium, whatever strikes your fancy), from which you can properly launch attacks and regroup when you need to. Then you take the time to seed one and only one entire segmentum with sleeper agents and well disguised servants to destabilize the Imperium's hold on that area. after sufficiant destabilization and corruption of the segmentum to make it open to the idea of change (i.e chaos) You attack the imperium with a traditional Black Crusade (mass invasions of Imperial planets, rending of Warp Barriers to let in daemons and such, and the like), staging this incursion at an area that the imperium nowhere near the segmentum you seeded with traitors. As someone already pointed out, The Imperiums apparently infinite armies and limitless resources will eventually stamp out this crusade, but make is so large that it will take a while. then, take your true Black crusade to Annex the Segmentum you seeded. you now control a major portion of the imperium. then you repeat.

I believe you have overlooked at least four obstacles that would make things... difficult, to say the least.

1. Eldar. With all their aloofness and seemingly small and ever-decreasing numbers, they have an annoying habit to be just 'around the corner'. And if there is a race out there that hates Chaos with every fibre of its being, it is the eldar. Their rangers and harlequins are bad enough on their own, but once your "hidden empire" would grow, it will attract the attention of farseers, and that will mean trouble. Sudden ork attacks, necrons coming out of the woodwork, and even Imperial armies stumbling upon your little enterprise seemingly by chance, to name but a few.

2. Imperial Inquisition. For all the arch-heretics this organization spawned, it remains nevertheless an effective tool for rooting out the agents of Chaos. Inquisitors are (generally) smart, determined, strong-willed and have infinite resources at their disposal. Sooner or later they will find out your fledgling cults and start digging. And keep in mind, the question here is not IF, but WHEN. And once it happens, it will be a race against time. Your hand will be forced and you will have to begin sooner than you are ready, or lose entire cult network. Forget the millenia, if your cults be able to remain hidden for a few hundred years, you might consider yourself lucky.

3. Chosen of Chaos. For better or worse, but there is no such thing as an army of Loyal, Obedient and Selfless champions of Chaos. On the contrary, each and every one of them is a 'thing in itself', obssessed with ideas of his own grandeur. At best, a few of them may share a common ultimate goal, but even so nothing would stop them from backstabbing each other on the way of achieving it. Chaos, after all, favors only the strongest. At some point some of your champions will screw up and be discovered by enemies or go on a killing spree to appease the Dark Gods, or accomplish some other idiocy... the result would ultimately be the same: his antics will draw the attention of the Imperium to your enterprise.

And once any one (or even all) of the above-stated events will come to pass, your secret will be revealed for all Imperium to see, and the fourth factor will come into play:

4. Imperium's size. Imperium can mobilize a force large enough to cover both Segmentums simultaneously. In fact, it has enough soldiers and starships to fight for all five Segmentums at once, and it does so successfully for the last ten thousand years.

I'm not saying the plan is doomed to failure, far from it. Indeed, it is tactically sound and has every chance to succeed. But you really should scale it down. Significantly. To take over an entire Segmentum (one fifth of the whole Imperium, no less) you would require hundreds of thousands of space marines, billions of mortal troops and hundreds of battlefleets. It is a campaign on a scale worthy of the Great Crusade; way out of league for the warriors of Chaos with their rather meagre resources. Besides, as with all plans, the probability of failure rises exponentially depending on the scope of operation. A scheme that is plausible on the scale of a single planet, will almost certainly fail when applied even to a sub-sector, not to mention a Segmentum

I agree with Erborn regarding the problems of actually invading the Imperium. A far better thing is probably to aim to make a single planet into a daemon world or draw it into the Warp than to gamble for anything larger than a small sub-sector. In regards to larger areas, the best way would probably be to make a sector of a few systems be isolated from the Imperium in some way or another. If you can somehow target the psychers or something and thus ensure that communications are lost, you can probably win a few decades or maybe a century to act before the Imperium returns.

My plan of attack would to keep things in the range of certain victories. Its better with a small certain victory than a large one that is in gamble. Thus make a name for yourself fighting for others or in smaller operations and gather a small cadree of people that you can rely on to support you in the long term and not backstabb you untill things really are ******. If you can survive long enough, make some contacts and most importantly make a name for yourself and get experienced then you can start to gather a warband. But in this, keep it simple and small. Gather a dozen desperados or something to raid a nearby warband's little holdout, and keep working like this and slowly build up scales. Only after several centuries would I dare to make my own Black Crusade, and that against a lone planet or a small sub-sector that I could be certain of both taking down quickly and escaping away from before the slaves of the Carrion God returns. Then, once back in the Screaming Vortex I would probably start to seed diversions and actual preperations for a future Black Crusade.

Here would be the way that I would make it happen.

1. Start by fighting for other warlords and warbands to get a reputation, contacts and start to make a name for yourself

2. Gather a few people that you can work with and that would stick around with you for long-term gain, and make sure that you can actually deliver gain to them and make service to you rewarding

3. When you've made a name for yourself, try and take over or create a warband of your own. Then make an even better/worse name for yourself with leading that warband successfully - it would also give you experience in leadership over followers of Chaos. Don't be afraid to get your warband along with others for a Black Crusade lead by other champions of Chaos, its more or less the same as mentioned in nr 1.

4. Once your warband has grown pretty good, you may start to think about doing raids against Imperial space, loot old Xenos ruins for useful artefacts and similar things.

5. If you've managed to survive this far, you should have some "trusted" lieutenants and likely at least a few thousand lowly followers at your command and equipment to arm and transport them, as well as experience with leading them. This is when, at the earlierst, that you can start to make moves to gather lesser warbands and warriors into a Black Crusade. Then take this attack and direct it against a good but takable target, like a single Forge World or Hive Worlds or a few other worlds. Make sure that you know what you do and want to do, and then retreat in good order. And always have a backup plan to get you the hell away from the Imperials if things goes to hell.

That's how I would do it anyway. Slow and steady.

Erborn said:

...Point taken. same concept, but subsectors.

Maybe the goal shouldn't be take down the Imperium as a whole, but rather deal with ancient grudges (or recent if the players were on the run from the Imperium in the first place).

Say if the players are Iron Warriors, then slipping out and scoring a major victory against the Imperial Fists would be grand. Say taking down their famous monastery-ship. Or if they are Thousand Sons, then burning Fenris or one of their protected worlds.

Or capture a single world. A valuable world that can provide resources to those with the vision to work towards taking down the Imperium.

The Imperium is weak in many areas: if I were atttempting to bring it down, I would adopt an approach of combining military "scorched earth" assaults on key agri worlds, perhaps with bioweapons, while increasing cult activity on adjacent hive and forge worlds. As the populance starts to starve, civil uprisings become all the more intense, leading to civil war, secession and chaos.

The Alpha Legion would be key to this kind of tactic, given their guerilla warfare specialty. A squad of Alpha Legionnaires in each Sector overseeing and coordinating a network of cults and agents would be more than sufficient to cause untold damage.

Aggressive campaigns like this, properly timed to coincide with each other in dozens of adjacent sectors, would place untold stress upon the Imperium's military and economic might.

With regard to Abaddon's overall plan, perhaps it is economic in nature: he wants the Imperium to collapse in the same way the Soviet Union did, by bankrupting it. Although traditional economics probably break down on a Galactic scale, the common people still need to be fed, or the rulers will be in trouble. The Imperium, like the Soviet Union in 1990, appears strong, but has deep cracks in its structure. Massive, constant, external pressure, both military and economic, could suddenly lead to so many individual uprisings that the Imperium would effectively cease to function. The wider Imperium would become Balkanised, Cadia cut off without the infrastructure to support it or send reinforcements, easy prey to true military intervention on a scale only the Chaos Legions can manage. Individual Sector Lords would start to look to the defence of their own realms and refuse to send miitary aid beyond their borders. The Imperium would shatter into thousands of petty empires, chaos would reign....

Lightbringer said:

Good plan! I also agree with the concept of having the Imperium breaking beneath the stress. Of course this requires alot of efforts it is most certainly something that will take alot of time and effort. Also taking appart the Imperium will be a job of one part at a time, and making the moves toward the targets that will matter in the long run. Like Agriworlds.