After the American Revolution, the English colonies acted more like independent republics than united states. Each began following its own path, which made eventual union very difficult to attain.
There was a weak governing body in the form of the national congress. All laws required 9 of 13 states to approve them, so very little was passed in the first few years after the revolution.
Each state also followed its own goals, some of which interferred with its neighbors. Connecticut and Pennslyvania nearly began a shooting war over a longstanding border dispute while Massachusetts and Virginia argued over lands in the west.
Each colony also began using a different currency. Some used pounds, some used Spanish dollars. Some even produced their own, so there was no uniform currency for them to enjoy.
Many of these differences stemmed from the colonies themselves. The New England colonies, who were more industrial favored strong duties on imports. The Southern colonies, who exported crops for a living, wanted to tariffs because it encouraged retaliatory tariffs from their importers.
These are just some of the differences it was diffcult to unite the county after the war.