Massive galaxies and galaxy clusters gain much of their mass by merging with their neighbors; this hierarchical structure formation is the foundation of our understanding of galaxy evolution. Nevertheless, the detailed evolutionary processes needed to form the structures we see in the local Universe remain poorly understood. This thesis comprises four projects examining the growth of galaxies and clusters at high redshift by using radio, sub/millimeter, and X-ray observations to provide empirical constraints on their cosmic evolution. Chapter 2 presents deep 1.2mm imaging of the inner 20' x 20' of the Lockman Hole North (LHN) field to search for submillimeter galaxies (SMGs), rapidly star-forming, high-redshift galaxy mergers. We detect 41 SMGs with S/N>4.0 and use Monte Carlo simulations to estimate their number counts and angular clustering properties. Chapter 3 investigates the nuclear accretion properties of the LHN SMGs. In the sample's average rest-frame X-ray spectrum, we detect strong Fe K alpha emission (equivalent width EW >=1 keV) from highly-ionized Fe species -- evidence that beneath the galaxies' heavy obscuration, supermassive black holes may be growing rapidly. Chapter 4 describes a new 345 GHz and 2.1 GHz imaging campaign to study the intracluster media (ICM) of eleven massive Sunyaev Zel'dovich Effect (SZE)-detected clusters from the Atacama Cosmology Telescope (ACT) southern survey. In six of eleven, 345 GHz SZE increments are detected and used to characterize the spatial distribution and energy content of the ICM at high (19.2") resolution. This work helps us understand how SZE-mass scaling relations are affected by contamination from other sources along the line of sight and by dynamical properties of the ICM. Chapter 5 studies the non-thermal radio emission in one exceptional z=0.8&0 binary cluster merger (ACTJ0102-4915, ``El Gordo'') with the help of newly-acquired radio observations. El Gordo is the highest-redshift cluster known to host double radio ``relics'' and a radio ``halo,'' and by characterizing the morphology, intensity, spectral index, and polarization of these structures, we extend our knowledge of ICM shocks and magnetic fields to an era when the Universe was only 50% its current age.