Rapid evolutionary radiations likely result from the combined effects of selective pressures and demographic processes. The songbird genus Junco of North America includes several phenotypically divergent northern forms which have arisen within the last 10,000 years as a result of a rapid postglacial expansion across North America. These northern forms contrast with more genetically divergent ancestral southern forms that are geographically isolated, yet show moderate phenotypic divergence. In addition to the role of geographic and historical factors, the wide range of habitat types and the highly diversified patterns of plumage coloration suggest the role of multiple selective factors in driving lineage divergence. Here we combine whole-genome and genotyping-by-sequencing (GBS) data to reconstruct the evolutionary history of the genus and explore how genomic patterns of variation relate to demographic events and selective factors. We use MSMC (multiple sequentially Markovian coalescent) and G-Phocs (generalized phylogenetic coalescent sampler) to test the population-expansion and recent-divergence hypotheses in northern junco forms. MSMC revealed recent demographic expansions for all the northern junco forms, reinforcing the hypothesis of multiple lineage differentiation driven by a postglacial northward recolonization of North America. We also used Bayescan to calculate FSTand posterior probabilities per SNP to infer selection-mediated divergence, and found no specific regions of high differentiation but rather a number of highly divergent variants scattered across the genome. This suggests the role of selection acting on numerous loci across the genome from the early stages of the speciation process. Our analyses show that juncos represent one of the fastest radiations documented in birds, with major roles for historical, demographic and selective factors.