The several states comprising the United States did act in a nationalistic way in prosecuting the Revolutionary War and securing freedom from Great Britain. They were unable to become unified under a truly nationalist system not because of distrust of their former government, but because of the sectional and regional differences which made up the country.
From the founding of the colonies, there were two distinct cultures in early America whose interests were quite disparate. The Southern Colonies were based on agriculture, primarily the production of large staple crops. This was geographically determined as the South had long growing seasons,fertile soils and a warm climate. The large investment in labor needed to make such a system work led to the widespread use of slavery. The North, to the contrary, had short growing seasons, thin rocky soils, and colder climates; but it did possess an excellent system of rivers and harbors which lent itself to shipping and later manufacturing.
The difference in economies became a defining characteristic of the nation. This disparity showed itself at the Constitutional Convention when Southern delegates threatened to walk out unless slavery were protected. After the government was formed, discussions over tariffs, important to the North but a bane to the South, occupied much political debate. It is not coincidental that it was primarily the southern states who supported a position of strong state governments vs. the northern position of a protective government.
These differences, endemic from the founding of the country, prevented the formation of a truly nationalistic approach.
Given the context, I assume that you are using the term "nationalism" to mean identifying with the country rather than with one's individual state. The lack of such national feelings was a problem in the time right after the US became independent. It was caused largely by fear and distrust of centralized government.
The colonies had rebelled against Britain in large part because they disliked being ruled by a distant government that did not seem to understand their needs. After independence, they worried that a national government would do the same thing. This sort of distrust of national governments was a major factor that prevented the US from developing a strong sense of nationalism in its early days.