  We show that the long-range rapidity correlations between the produced
charged-hadron pairs from two BFKL parton showers generate considerable
azimuthal angle correlations. These correlations have no 1/N_c suppression. The
effect of gluon saturation on these correlations are discussed and we show that
it is important. We show that a pronounced ridge-like structure emerges by
going from the BFKL to the saturation region. We show that the ridge structure
at high-energy proton-proton and nucleus-nucleus collisions has the same origin
and its main feature can be understood due to initial-state effects. Although
the effects of final-state interactions in the latter case can be
non-negligible.
