The theory of supergravity suggested a novel approach to unification. Supergravity constitutes an extension of general relativity, allowing to make the same predictions for the classical tests. The fundamental reason is that supergravity brings together several of the most fundamental concepts in modern physics and hence it achieves more than any earlier quantum theory of gravity. It is important to remember that physical theories are guided by principles of symmetry. A symmetry can be either global or local form.
Important examples are theory of general relativity and electromagnetism.
If a set of physical laws is invariant, the stronger requirement of invariance under local symmetry can only be met by introducing new fields. This then means new forces. The fields are called gauge fields and correspond to new particles whose exchange gives rise to the corresponding forces. A fundamental example is gravitation. Gravity is the gauge field of local Poincare invariance and the gravitational force results from the requirement that Poincare symmetry be local.