  It has been suggested that unresolved radio galaxies and radio quasars
(sometimes referred to as misaligned active galactic nuclei) could be
responsible for a significant fraction of the observed diffuse gamma-ray
background. In this study, we use the latest data from the Fermi Gamma-Ray
Space Telescope to characterize the gamma-ray emission from a sample of 51
radio galaxies. In addition to those sources that had previously been detected
using Fermi data, we report here the first statistically significant detection
of gamma-ray emission from the radio galaxies 3C 212, 3C 411, and B3 0309+411B.
Combining this information with the radio fluxes, radio luminosity function,
and redshift distribution of this source class, we find that radio galaxies
dominate the diffuse gamma-ray background, generating $77.2^{+25.4}_{-9.4}\%$
of this emission at energies above $\sim$1 GeV. We discuss the implications of
this result and point out that it provides support for scenarios in which
IceCube's high-energy astrophysical neutrinos also originate from the same
population of radio galaxies.
