Final answer:
The events listed in the timeline are best grouped as the Nationhood era, marking the United States' transition to an independent nation with its own government and constitutional framework.
Step-by-step explanation:
The historical era that best groups the event in the timeline is the Nationhood era. This period includes the Declaration of Independence in 1776, the establishment of the first national government with the Articles of Confederation in 1781, the end of the American Revolution in 1783, the passage of the U.S. Constitution by the Federal Convention in 1787, North Carolina's ratification making it the 13th state to join in 1790, and the passing of the Bill of Rights in 1791.
These events reflect the United States' transition from a set of colonies to an independent nation with its government and constitution, embodying the principles of self-governance and federalism.