1. Good agriculture, as well as harbours and river systems, allowed colonists to sell crops and other goods; balanced economy
The Middle Colonies had very fertile soil, which made them an exporter of wheat and other grains. The land was also much cheaper than in Europe, which encouraged new arrivals that contributed to the diversity of the area.
2. The Dutch
Much of the area of the Middle Colonies was part of New Netherland until the British captured the territories in their war with the Dutch in 1664. The majority of the conquered land became the province of New York.