A three-dimensional polybead model of the structure and large strain deformation of amorphous polymeric networks is constructed and evolved via Monte Carlo techniques. The model has successfully simulated various deformation conditions and been found to qualitatively capture the proper state of deformation, rate of deformation, and temperature dependence of real amorphous polymeric materials. Partitioning of the stress calculations indicates that strain softening following yield is a result of the evolution of intermolecular contributions to the response whereas the strain hardening phenomenon is a result of evolution in the intramolecular contributions. These calculations provide a fundamental basis for development of continuum-level plasticity models and, indeed, support assumptions currently used in successful constitutive models of the elastic-viscoplastic behavior of polymers.