Why were the Middle Colonies founded?

The Middle Colonies were founded to work as a buffer between New England and Spanish-controlled Florida. Next to Great Britain, Spain was a major colonial power and a competitor in the establishment of influence in the western hemisphere. Fearing the Spanish would attempt to expand further and move north from Florida, officials in the British government formed the Middle Colonies as a barrier.
Additionally, the Middle Colonies were founded to provide greater agricultural opportunities. The land in the northern colonies was not fit for mass farming—the first settlers of Jamestown suffered from prolonged famines—and the mountainous terrain did not provide the open, fertile land needed to yield harvests. With the establishment of the Middle Colonies, farmers moved south and began to produce major cash crops such as cotton, tobacco, and grain.