Before Hitler came to power, Harry H. Laughlin laid the blueprint. This book is a forensic investigation into how one American scientist-backed by the Carnegie Institution-helped shape the ideology and infrastructure of eugenics both in the United States and Nazi Germany. Laughlin's legislative fingerprints appear on the Immigration Act of 1924, anti-miscegenation laws, state sterilization policies, and ultimately, the eugenic portions of Hitler's infamous Nuremberg Racial Decrees.With access to forgotten archival sources and primary documents largely overlooked, A.E. Samaan reconstructs a web of influence that spans elite universities, international congresses, prestigious institutions, and wartime propaganda disguised as mainstream science. More than a biography, this book is a reckoning of the deep roots of National Socialism's eugenics on American soil. For readers of Edwin Black, Robert Proctor, and Timothy Snyder, this meticulously documented work reveals how a "progressive" American science became a transatlantic engine of exclusion, sterilization, and genocide-and why history must never forget its original architects.