From [General Relativity][1] edited by Stephen Hawking:

>This is to be used to generate a perturbation series in powers of $GE^2$ or $G/r^2$ (where $E$ and $r$ are an energy and a length that are characteristic of the process under study)

From [Quantum Field Theory in a Nutshell][2] by Zee:

>We come to the same morose conclusion that the theory of gravity, just like Fermi’s theory of weak interaction, is nonrenormalizable. To repeat the argument, if we calculate graviton-graviton scattering at energy E, we encounter the series  
~ $[1+ G_NE^2 + (G_NE^2)^2 + ...]$.

I'm just looking for a brief explanation for this type of expansion or some resource where I can understand why it is in this specific form.


  [1]: https://www.cambridge.org/gb/universitypress/subjects/physics/cosmology-relativity-and-gravitation/general-relativity-einstein-centenary-survey-1?format=WX&isbn=9780521137980
  [2]: https://press.princeton.edu/books/hardcover/9780691140346/quantum-field-theory-in-a-nutshell