During the British Colonial period in the United States, most of the economic activity and population was concentrated on the North-East of the Continent.
This is where the first 13 colonies were established.
The reasons were simple:
1. All colonies were near the Atlantic Ocean and had relatively easy sea access to Britain.
2. Ports helped to maintain economic activity, import/export and slave trade
3. The colonies were sparsely populated compared to England, and colonists were busy in setting up plantations, infrastructure etc.
Throughout the 17th century the population of Europeans in North America was around 250,000 and peaked at 2.5 million by 1776