Bone Thugs and Wu were scheduled to release an entire album together in '96. Something happened (yeah it was layzie's dude got into some issue with someone from Wu) and it collapsed. Then the RZa and GZA intro on Forever disc 2 was done, and even though that probably wasnt aimed at Bone Thugs, Krayzie thought it mightve been , and then released the song "aint saying no names" that clearly was aimed at RZA.
Beef has all been squased though since, some bullshit.
Gotta remember Bizzy was on Wu's dick for a while, he got a crew together in mid 90's with NY rappers that were very reminiscent of Wu style (like his sidekick Mr Majesty), so it is weird it never happened.