  One way to understand the nonthermal history of the universe is by
establishing the origins of the unresolved and truly diffuse extragalactic
gamma rays. Dim blazars and radio/gamma galaxies certainly make an important
contribution to the galactic gamma-ray background given the EGRET discoveries,
and previous treatments are reviewed and compared with a new analysis. Studies
of the gamma-ray intensity from cosmic rays in star-forming galaxies and from
structure formation shocks, as well as from dim GRBs, are briefly reviewed. A
new hard gamma-ray source class seems required from the predicted aggregate
intensity compared with the measured intensity.
