Flight is a key evolutionary innovation in insects that has shaped their extraordinary diversity on Earth. Paradoxically, secondary flight loss is widespread across the insect tree of life and has been documented in nearly all insect orders. Although the consequences of flightlessness have been explored under a wide range of hypotheses, the possibility of flight reacquisition has been marginalized and deemed unlikely. This thesis investigates the interplay between wing morphology, flightlessness, and diversification processes in the ground beetle genus Calosoma Weber, 1801 (Coleoptera: Carabidae: Carabinae). This cosmopolitan lineage contains both flight-capable and flightless species within an otherwise flightless subfamily. To date, the lack of a robust and comprehensive phylogeny has hindered rigorous evaluation of wing evolution in Calosoma. To address this knowledge gap, I adopt an integrative genomic-scale approach that combines population genomics, phylogenomics, and macroevolutionary analyses, leveraging the untapped potential of natural history museum collections. I develop a new methodological pipeline to integrate diverse genomic datasets and improve phylogenetic inference in the beetle suborder Adephaga, thereby refining the phylogenetic placement and temporal origin of Carabinae. At the microevolutionary scale, I conduct population genomic analyses of flightless Calosoma lineages, which highlight contrasting evolutionary trajectories shaped by orogenies and climate change. At the macroevolutionary scale, I infer a robust and comprehensively sampled phylogenomic timetree of Calosoma, identifying clades necessitating parallel taxonomic revisions. Estimates of divergence times and ancestral ranges place the origin of Calosoma in the Holarctic region during the late Eocene, followed by a dynamic dispersal-driven colonization of tropical latitudes in the Oligocene and Miocene. Reconstructions of ancestral wing morphology support a fully winged ancestral condition in Calosoma followed by repeated wing reduction events, and several potential instances of secondary fully developed wing reacquisition. Relying on comparative analyses, I show that while flight capability is closely associated with the biogeographical history of Calosoma beetles, it does not correlate with diversification rates. In this thesis, I establish Calosoma as an excellent model system to study wing morphology evolution while also proposing a multi-scale evolutionary scenario explaining its current diversity.