Rapid adaptation is aiding invasive populations in their competitive success. The evolution of increased competitive ability (EICA) hypothesis posits this enhanced performance results from escape from native enemies, yet its support is equivocal. We here test EICA comprehensively by investigating adaptive divergence of various constitutive and inducible defence-related traits within the native North America and introduced European and Australian ranges, whilst controlling for divergence due to latitudinal trait clines, individual resource budgets and population differentiation using >11,000 SNPs. We do not identify a general reduction in defence in concert with an increase in growth among the multiple introduced ranges as predicted by EICA. Yet, rapid, repeated clinal adaptation in defence-related traits was apparent despite distinct demographic histories. Divergence in energy budgets among ranges may explain some, but not all, defence-related trait divergence. Synthesis: The rapid spread of invasive species is affected by a multitude of factors, likely including adaptation to climate and escape from natural enemies. Unravelling the mechanisms underlying invasives’ success enhances understanding of eco-evolutionary theory and is essential to inform management strategies in the face of ongoing climate change.