can anyone think of a good map-based campaign story line, has to incluide Chaos (iron warriors), Eldar (ulthwe), Tau and maybe imerial guard or traitor guard...
i need to start it soon so can someone please come up with a storyline?
be imaginative...

The Iron Warriors like all things techy so a warsmith hears of the Tau and there uber tech and decides "hey i want me some of that" and arranges to attack a small tau outpost in order to wipe it would and study their tech in the hopes to make it their own. They land a ship and start using it as a bse of operations on the Tau world.

The eldar have this habit of helping out the Tau from time to time so it would be easy to say the farseer has seen that the tau are needed in the future and so move to support them via a hidden web way gate, although indirectly cos you know the eldar dont want people to know as there all misterious and stuff.

In order to facilitate helping the Tau, the eldar attract the attention of a near by imperial world by shooting up some of their ships and making it look like the work of chaos. IG conviently set out to hunt said chaos renegade scum down and theres this trail that leads to some xenos planet where they find the IWs setting up some kind of base. Its clearly a fortification from where they intend to raid other imperial worlds so the IG drop in and set up a forward attack post just out of range of the IWs. The tau promptly see them and think their invading and the Imperium promtly see the tau and decide to wipe out the Xenos scum while there here.

then the shooting begins.

As for the map you have 4 main locations to act as starting points for the armies, the IW shipfort, the IG dropzone, the Eldar webwaygate and the Tau outpost.

Eldar can always be relied upon to give you a nice objective: the spirit stone of a great Farseer/a crashed Eldar ship carrying some arcane artefact/any other item of incredible importance, imprisoned in said crashed ship or some ancient vault. This can be in the centre of your map: give your players four equidistant starting points, and a campaign turn limit. Whoever possesses the location on the last turn wins.

Motivations:
Eldar want their magical doohickey, whatever it is, back.
IG are defending their home planet, which happens to be the one on which the ancient artefact is locked away/has crashed.
IW want the Eldar's magical doohickey, being daemon-worshippers...
Tau are following the trail of the IW, who ploughed through Tau space en route to their objective.

thanks guys any other ideas?