Energetic material (EM) composites subjected to mechanical or thermal loading can incite responses over a wide range of spatial and temporal scales due to the microstructural heterogeneities present within the sample, e.g., voids, inclusions, defects in and between grains, or composition variability, such as mixtures, additives and fillers. Simulating EMs with complex microstructure is a grand challenge, where until recently, an inherent gap in computational capabilities has existed in modeling grain-scale effects at the microscale. Many energy transfer processes within these materials are dominated by atomistic events, yet the overall material response is manifested at the micro- and mesoscale – scales beyond those amenable to atomistic simulation techniques. Moreover, continuum scale simulations can depict macroscale events; however, these simulations lack the fidelity to properly include material microstructure that influences the overall process. Particle-based microscale simulation methods that utilize coarse-grain models offer a promising route for extending the attributes of atomistic modeling toward the microscale. Coarse-graining, a term used across a wide range of communities, can be generally defined as the simulation of models at length and/or time scales that would not be practical to simulate using atomistic models, yet simulating at the continuum level cannot be justified since the material is not sufficiently homogeneous. In this work, the development of such microscale models and methods based upon the energy-conserving dissipative particle dynamics method is discussed. A variety of simulated composite microstructures will be presented, including samples with intra- and inter-granular voids of varying shape, size and relative orientation, varying grain shapes and sizes, polymer binder, and gas-filled inclusions.