In early part of American history, it feels like Boston and Philadelphia are the cities at the center of it all, where everything big happens happens. However, in the modern era, NYC is by far the largest city on the East Coast (population of 8 mil) while Philly (1.5 mil) and Boston (600k) are now much smaller. When and how did this transition take place and what caused it to happen?
A few reasons:
Geographical determinism: Long Island and Staten Island protect the harbor (the southernmost tip of Manhattan was easily defended in case of attack), the deep water port produces less ice than shallower ports (i.e., Boston), and the construction of the Erie Canal, as mentioned already, provided a connection to the Midwest and the Great Lakes.
European politics: the British, resentful for having lost their colonies, preferred not to trade with revolutionary cities (i.e., Boston). Thus, after the War of 1812, New York became a dumping ground for European goods.
A lot of capital-intensive industries that relied on imported raw materials (i.e. sugar refining and garments) ended up there for reasons 1 and 2. And since the first few garment/sugar factories arose in NYC, this attracted more sugar/garment workers to the city, which in turn attracted more industrialists looking to build sugar/garment factories, etc. In a phrase, "cumulative causation" due to high transportation costs, a need for specialized employees that already were based in the city, and relatively minor comparative advantages that compounded over time.
Sorry if this isn't clear, I'm a little drunk, my source is what I can remember from Edward Glaeser's article "Urban Colossus" (Warning, PDF:http://scholar.harvard.edu/files/glaeser/files/hier2073.pdf) EDIT: Grammar
I'd like to add a question in a similar vein, if I could.
Chicago was established long before LA, yet LA has grown larger than Chicago. Is there any explanation other than weather that accounts for this?
(I tried posting this on its own, but received no answer)