We compare ${\ensuremath{\sigma}}_{R}(E)$ for nucleus-nucleus systems (obtained from existing direct measurements and derived from elastic scattering data) with nucleon-nucleon and nucleon-nucleus data. The energy dependence of ${\ensuremath{\sigma}}_{R}(E)$ for nucleus-nucleus systems is found to be quite rapid; there appears to be no evidence for an energy independent, geometric ${\ensuremath{\sigma}}_{R}$. Simple parameter free microscopic calculations are able to quantitatively reproduce the data and thus, emphasize the dominance of nucleon-nucleon interactions in medium energy nucleus-nucleus collisions.NUCLEAR REACTIONS Total reaction cross section theory, comparison to data for $d$, $^{3}\mathrm{He}$, $\ensuremath{\alpha}$+$^{12}\mathrm{C}$, $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, $^{208}\mathrm{Pb}$ and $^{12}\mathrm{C}$+$^{12}\mathrm{C}$. Predictions for $^{40}\mathrm{Ca}$+$^{40}\mathrm{Ca}$, $^{40}\mathrm{Ca}$+$^{208}\mathrm{Pb}$, $^{208}\mathrm{Pb}$+$^{208}\mathrm{Pb}$. Energy range $3l{E}_{\frac{i}{n}}l1000$ MeV.