The split between the two forces (the symmetry breaking) is due to another field, called the Higgs field, which gives the W and Z particles mass while leaving the photon massless. This unification means that, at a fundamental level, the four forces of nature are reduced to just three: the electroweak force, the strong nuclear force, and gravity (which in any case is not actually a force at all, according to general relativity). You may disagree with me as to whether this has helped simplify matters.
