Advancing transportation quickly led to settlement of the fertile Mohawk and Gennessee valleys and the Niagara Frontier. Buffalo and Rochester became boomtowns. Significant migration of New England "Yankees" (mainly of English descent) to the central and western parts of the state led to minor conflicts with the more settled "Yorkers" (mainly of German, Dutch, and Scottish descent). More than 15% of the state's 1850 population had been born in New England . The western part of the state grew fastest at this time. By 1840, New York was home to seven of the nation's thirty largest cities.