The economic conditions that necessitate the construction of very high buildings on narrow lots first emerged as a decisive factor in New York City. Intensive land use, with the resulting speculative traffic in real estate, was itself a consequence of more powerful and pervasive forces. Industrial expansion was the primary factor, and in the period following the American Civil War much of that expansion continued to be concentrated in New England and the Middle Atlantic states. Financial institutions had long been located mainly in Boston, but the center was rapidly shifting to New York around the time of the War. A new pattern of close interdependence among industries demanded centralization of business administration. The leadership of New York City as an ocean port, along with its proximity to major arteries of land transportation, was a local factor that helped to make the city an irresistible magnet. Its power to attract, once established, has never waned; even today it is a primary administrative and banking center. The financial resources for the high building were there; the development of safe elevator transportation and the organization of construction facilities soon made them a reality.