AbstractHelicobacter pyloriis a common component of the human stomach microbiota, possibly dating back to the speciation ofHomo sapiens. A history of pathogen evolution in allopatry has led to the development of genetically distinctH. pylorisubpopulations, associated with different human populations, and more recent admixture amongH. pylorisubpopulations can provide information about human migrations. However, little is known about the degree to which someH. pylorigenes are conserved in the face of admixture, potentially indicating host adaptation, or how virulence genes spread among different populations. We analyzedH. pylorigenomes from 14 countries in the Americas, strains from the Iberian Peninsula, and public genomes from Europe, Africa, and Asia, to investigate how admixture varies across different regions and gene families. Whole-genome analyses of 723H. pyloristrains from around the world showed evidence of frequent admixture in the American strains with a complex mosaic of contributions fromH. pyloripopulations originating in the Americas as well as other continents. Despite the complex admixture, distinctive genomic fingerprints were identified for each region, revealing novel AmericanH. pylorisubpopulations. A pan-genome Fst analysis showed that variation in virulence genes had the strongest fixation in America, compared with non-American populations, and that much of the variation constituted non-synonymous substitutions in functional domains. Network analyses suggest that these virulence genes have followed unique evolutionary paths in the American populations, spreading into different genetic backgrounds, potentially contributing to the high risk of gastric cancer in the region.