What does "it" refer to?

Does " took its place" refer to "took the place of unitarity"?

Context:

OF COURSE, I wasn't aware of all this when I began my research. But I felt that the study of elementary particles at that time was too like botany. Quantum electrodynamics-the theory of light and electrons that govens chemistry and the structure of atoms-had been worked out completely in the 1940s and 1950s. Attention had now shifted to the weak and strong nuclear forces between particles in the nucleus of an atom, but similar field theories didn't seem to work to explain them. Indeed, the Cambridge school, in particular, held that there was no underlying field theory. Instead, everything would be determined by unitarity-that is, probalility conservation-and certain characteristic patterns in the scattering of particles. With hindsight, it now seems amazing that it was thought this approach would work, but I remember the scorn that was poured on the first attempts at unified field theories of the weak nuclear forces, which ultimately took its place. The analytic S-matrix work is now forgotten, and I'm very glad I didn't start my research in elementary particles. None of my work from that period would have survived.

-Hawking My Brief History