  In a popular class of models, dark matter comprises an asymmetric population
of composite particles with short range interactions arising from a confined
nonabelian gauge group. We show that coupling this sector to a well-motivated
light mediator particle yields efficient darkleosynthesis, a dark-sector
version of big-bang nucleosynthesis (BBN), in generic regions of parameter
space. Dark matter self-interaction bounds typically require the confinement
scale to be above \Lambda_{QCD}, which generically yields large
(>>MeV/dark-nucleon) binding energies. These bounds further suggest the
mediator is relatively weakly coupled, so repulsive forces between dark-sector
nuclei are much weaker than coulomb repulsion between standard-model nuclei,
which results in an exponential barrier-tunneling enhancement over standard
BBN. Thus, dark nuclei are easier to make and harder to break than visible
species with comparable mass numbers. This process can efficiently yield a
dominant population of states with masses significantly greater than the
confinement scale and, in contrast to dark matter that is a fundamental
particle, may allow the dominant form of dark matter to have high spin > 3/2.
