In the present paradigm of the merger-driven galaxy evolution scenario, gas-rich spirals interact and merge before a quasar emerges and a giant elliptical results. It is during the merging stage that starburst and/or AGN activities are triggered, leading to an infrared luminous stage of galaxy mergers. Therefore, the local luminous and ultraluminous infrared galaxies ((U)LIRGs) provide the ideal nearby, extreme environments in which we study black hole accretion, AGN feeding and feedback, and the nature of star formation in starbursts, the connection among which remains poorly understood due to limitations of previous instrumentation. In this talk, I will present high-resolution submillimeter and near-infrared integral-field data cube of the nuclei in several (U)LIRGs at different stages of interaction taken with the Submillimeter Array (SMA) and Keck Telescopes on Mauna Kea. At the distances of these local mergers, our SMA very-extended and Keck laser guide star adaptive optics (LGS AO) observations probe the physical conditions of the centers of these systems at the scale of ~100s pc. Our results give a detailed description of the molecular gas kinematics as well as AGN/starburst activities in the nuclear region of these merging systems, and paint an overall picture of the evolution of the energetics in (U)LIRGs as the merger sequence progresses.