Adding a bit of history to the other comments: Bazaar is actually a successor to an earlier DVCS, called Gnu Arch (or Tom Lord's Arch, TLA, at some point). It started out in 2001 and was, I believe, the first of the DVCS crowd. It had some idiosyncrasies, but was a huge step up from CVS in terms of its principles.

tla was forked into baz (previously Bazaar), and bzr (previously Bazaar-NG) was a rewrite taking into account lessons learned from tla/baz. Darcs is yet another DVCS inspired partly by Gnu Arch.

So while the explosion of new DVCS around 2005 can definitely be traced back to the Bitkeeper incident, I believe the seed for modern DVCS was laid a bit earlier, in 2001, with Tom Lord's Arch. I think Gnu Arch/tla is to be credited with originally introducing many of the concepts of distributed version control.

Of course, if anyone knows of earlier history on distributed VCS or a VCS that isn't in some way a spiritual successor to TLA I would be quite interesting in knowing that.