  We study formation and evolution of bar-disk systems in fully self-consistent
cosmological simulations of galaxy formation in the LCDM WMAP3 Universe. In a
representative model we find that the first generation of bars form in response
to the asymmetric dark matter (DM) distribution (i.e., DM filament) and quickly
decay. Subsequent bar generations form and are destroyed during the major
merger epoch permeated by interactions with a DM substructure (subhalos). A
long-lived bar is triggered by a tide from a subhalo and survives for ~10 Gyr.
The evolution of this bar is followed during the subsequent numerous minor
mergers and interactions with the substructure. Together with intrinsic
factors, these interactions largely determine the stellar bar evolution. The
bar strength and its pattern speed anticorrelate, except during interactions
and when the secondary (nuclear) bar is present. For about 5 Gyr bar pattern
speed increases substantially despite the loss of angular momentum to stars and
cuspy DM halo. We analyze the evolution of stellar populations in the bar-disk
and relate them to the underlying dynamics. While the bar is made mainly of an
intermediate age, ~5-6 Gyr, disk stars at z=0, a secondary nuclear bar which
surfaces at z~0.1 is made of younger, ~1-3 Gyr stars.
