Iwasawa (1969) was partly motivated by an analogy with Weil's description of the zeta function of an algebraic curve over a finite field in terms of eigenvalues of the Frobenius endomorphism on its Jacobian. In this analogy,
The action of the Frobenius corresponds to the action of the group Γ.
The Jacobian of a curve corresponds to a module X over Γ defined in terms of ideal class groups
The zeta function of a curve over a finite field corresponds to a p-adic L-function.
Weil's theorem relating the eigenvalues of Frobenius to the zeros of the zeta function of the curve corresponds to Iwasawa's main conjecture relating the action of the Iwasawa algebra on X to zeros of the p-adic zeta function.