To add a bit to what Mad Scientist wrote:
The flying wing (the extreme example of a delta wing) is not an inherently stable platform. As a result, the original flying wing bomber (YB-35) made a lousy bombing platform since it wasn't stable enough.
With the advent of FBW, and computers that can automatically adjust control surfaces many times per second, inherently unstable aircraft have become feasible - e.g. the B-2.