The period 1965–1980 saw constraint handling in nonlinear programming pivot toward penalty-based reformulations and sequential strategies. Researchers emphasized turning constrained problems into sequences of unconstrained ones by penalizing violations, enabling unified treatment of constraints and stimulating later augmented Lagrangian ideas and interior-point concepts. The development of general frameworks for decomposing constrained problems into sequential unconstrained minimization problems aided the spread of penalty and SUMT-type approaches and connected to barrier and multiplier methods.