  Strong (sublattice or tower) formulations of the Weak Gravity Conjecture
(WGC) imply that, if a weakly coupled gauge theory exists, a tower of charged
particles drives the theory to strong coupling at an ultraviolet scale well
below the Planck scale. This tower can consist of low-spin states, as in
Kaluza-Klein theory, or high-spin states, as with weakly-coupled strings. We
provide a suggestive bottom-up argument based on the mild $p$-form WGC that,
for any gauge theory coupled to a fundamental axion through a $\theta F \wedge
F$ term, the tower is a stringy one. The charge-carrying string states at or
below the WGC scale $g M_\mathrm{Pl}$ are simply axion strings for $\theta$,
with charged modes arising from anomaly inflow. Kaluza-Klein theories evade
this conclusion and postpone the appearance of high-spin states to higher
energies because they lack a $\theta F \wedge F$ term. For abelian Kaluza-Klein
theories, modified arguments based on additional abelian groups that interact
with the Kaluza-Klein gauge group sometimes pinpoint a mass scale for charged
strings. These arguments reinforce the Emergent String and Distant Axionic
String Conjectures. We emphasize the unproven assumptions and weak points of
the arguments, which provide interesting targets for further work. In
particular, a sharp characterization of when gauge fields admit $\theta F
\wedge F$ couplings and when they do not would be immensely useful for particle
phenomenology and for clarifying the implications of the Weak Gravity
Conjecture.
