In this paper, we show that a cluster expansion approach provides a common starting approach for several key classes of coacervate theory currently in the literature. We build off the standard approaches taken by Mayer to derive Debye-Hückel theory using cluster expansions, 115 and thus re-derive Voorn-Overbeek; 66,67 however, we show that variations of this approach can be used to justify several other models spanning polymer field theory and ion pairing theories. We show how different choices of approximation, presented in the context of cluster expansions, give rise to the different models and particularly why linear charge density is such an important variable for model selection. We can then develop a metric to quantify the boundary between high charge-density and low charge-density approaches.