  Ultrahigh-energy string scattering is investigated to clarify the relative
role of string and gravitational effects, and their possible contributions to
nonlocal behavior. Different regimes can be characterized by varying the impact
parameter at fixed energy. In the regime where momentum transfers reach the
string scale, string effects appear subdominant to higher-loop gravitational
processes, approximated via the eikonal. At smaller impact parameters,
"diffractive" or "tidal" string excitation leads to processes dominated by
highly excited strings. However, new evidence is presented that these
excitation effects do not play a direct role in black hole formation, which
corresponds to breakdown of gravitational perturbation theory and appears to
dominate at sufficiently small impact parameters. The estimated amplitudes
violate expected bounds on high-energy behavior for local theories.
