2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54089In this talk, delivered at the Oscar Klein Centenary Symposium in Stockholm, I review the 1938 conference held in Warsaw devoted to \lq \lq New Theories in Physics". I review all of the talks presented at this meeting and discuss in detail Klein's paper where he proposed a unified model of electromagnetism and the nuclear force that foreshadowed the later developments of non-Abelian gauge theories.A talk delivered at the Oscar Klein Centenary Symposium, 46 pages plus 1 uuencoded eps figuresHigh Energy Physics - Theorytext