  Why do some clusters have cool cores while others do not? In this paper,
cosmological simulations, including radiative cooling and heating, are used to
examine the formation and evolution of cool core (CC) and non-cool core (NCC)
clusters. Numerical CC clusters at z=0 accreted mass more slowly over time and
grew enhanced cool cores via hierarchical mergers; when late major mergers
occurred, the CCs survived the collisions. By contrast, NCC clusters of similar
mass experienced major mergers early in their evolution that destroyed
embryonic cool cores and produced conditions that prevent CC re-formation. We
discuss observational consequences.
