While I know this plant is spotted knapweed (Centaurea stoebe ssp. micranthos, Asteraceae), there seems to be some confusion about the specific taxonomy. Most authorities seem to list it as C. stoebe ssp. micranthos but others call it C. maculosa. According to the USDA they’re synonymous, but I don’t know the source of the conflicting nomenclature.
There are perhaps 600 known species in this genus, and some of them are native here in southern Michigan. This particular knapweed is an invasive species. It was probably introduced from Europe in contaminated seed in the late nineteenth century, and has since spread across the continent. It gets a foothold in disturbed areas, and once established it can outcompete native plants and spread rapidly. Biocontrol agents have been used to fight this invasive, including weevils, flies, and moths.