In a joint work with S. Ibrahim, we use the idea of ground states and excited states in nonlinear dispersive equations (e.g. Klein-Gordon and Schr\"odinger equations) to characterize solutions in the N-body problem with strong force under some energy constraints. Indeed, relative equilibria of the N-body problem play a similar role as solitons in PDE. I will introduce the ground state and excited energy for the general N-body problem and give a conditional dichotomy of the global existence and singularity below the excited energy. This dichotomy is given by the sign of a threshold function. I will also talk about a restricted 3-body problem (Hill's lunar type problem) that has a very nice analogy to the nine-set theorem studied by Nakanishi-Schlag on NLKG.