We show that for each prime p congruent to 1 (mod 8), there exists a threefold Xp such that the existence of certain rational points on Xp produces
families of generalized Mordell curves and of generalized Fermat curves
that are counterexamples to the Hasse principle explained by the
Brauer–Manin obstruction. We also introduce a notion of the descending
chain condition (DCC) for sequences of curves, and prove that there are
sequences of generalized Mordell curves and of generalized Fermat curves
satisfying DCC.