Founded in 2010, the Unity project started by Mark Shuttleworth and
Canonical has gone on to deliver a consistent user experience for
desktop and netbook users alike. Putting great design at the heart of
the project, Unity and its technologies such as Application
indicators, System indicators, and Notify OSD, have strived to solve
common problems in the Free Software desktop while optimizing the
experience for touch, consistency and collaboration.

Courtesy: http://unity.ubuntu.com/about/

As to the reason for the splitup:

Canonical made the switch for the next release of its Ubuntu desktop
Linux distribution, because of increasingly divergent views of how a
desktop interface should look and operate, according to Canonical
founder Mark Shuttleworth.

You can read in detail at:
http://www.pcworld.com/article/208708/article.html