  String theory has long ago been initiated by the quest for a theoretical
explanation of the observed high-energy ``Reggeization'' of strong interaction
amplitudes. In terms of quantum field theory, it is the so-called ``soft''
regime, where the coupling constant is expected to be large and thus
perturbative calculations inadequate. However, since then, no convincing
derivation of the link between gauge field theory at strong coupling and string
theory has come out. This 35-years-old puzzle is thus still unsolved. We
discuss how modern tools like the AdS/CFT correspondence give a new insight on
the problem by applying it to two-body elastic and inelastic scattering
amplitudes. We obtain a geometrical interpretation of Reggeization and its
relation with confinement in gauge theory.
