The Real Reason Delaware Separated From Pennsylvania

It's hard to imagine, but Delaware didn't exist as a separate colony during early American history. The area passed through many hands in the beginning, from the Swedes to the Dutch to the British (with a brief return to the Dutch in 1673) (via Britannica). The Duke of York treated the land as a part of the colony of New York until he gave it to William Penn, the proprietor of the Pennsylvania colony. This move gave Penn access to the ocean, which was important for trade. 

Penn's colony basically then was made up of two distinct entities: the Upper Counties of Bucks, Chester and Philadelphia, and the Lower Counties on the Delaware, of New Castle, Kent, and Sussex (via History). Penn tried to unite the people of the three Upper Counties and the newly added Lower Counties, according to the Delaware General Assembly. But his efforts failed, as neither side was interested in joining forces. Penn eventually admitted defeat, and each set of counties was allowed to create its own legislature of elected officials. The Delaware counties held their first meeting of their independent government in 1704. But even with their separate political body, these counties still remained part of Pennsylvania, as both of the Upper and Lower Counties shared the same governor. It would take a revolution for Delaware to become its own entity.