  We consider weakly-coupled theories of massive higher-spin particles. This
class of models includes, for instance, tree-level String Theory and Large-N
Yang-Mills theory. The S-matrix in such theories is a meromorphic function
obeying unitarity and crossing symmetry. We discuss the (unphysical) regime
$s,t \gg 1$, in which we expect the amplitude to be universal and exponentially
large. We develop methods to study this regime and show that the amplitude
necessarily coincides with the Veneziano amplitude there. In particular, this
implies that the leading Regge trajectory, $j(t)$, is asymptotically linear in
Yang-Mills theory. Further, our analysis shows that any such theory of
higher-spin particles has stringy excitations and infinitely many
asymptotically parallel subleading trajectories. More generally, we argue that,
under some assumptions, any theory with at least one higher-spin particle must
have strings.
