In cylindrical geometry, we analyze the hypothesis that the major disruption in tokamaks is due to the interaction of tearing modes of different pitch. For a flat safety factor profile, we find that the m = 3/n = 2 tearing mode, which is linearly unstable, is strongly destabilized nonlinearly by the m = 2/n = 1 mode. Other modes are nonlinearly destabilized, particularly the m = 1/n = 1 and m = 5/n = 3 modes. Due to the development of islands of many different pitches, the toroidal current density profile is severely deformed. The corresponding region of island activity can extend essentially from the plasma center to the limiter. Presumably, this deformation of the field lines can lead to rapid transport of heat and particles from the plasma center to the limiter. The destabilization of the m = 3/n = 2 mode and other odd m modes is significant because it may correspond to the observed vertical asymmetry of some of the major disruptions in PLT.