Explanation:
The United States has operated under two constitutions. The first, The Articles of Confederation, was in effect from March 1, 1781, when Maryland ratified it. The second, The Constitution, replaced the Articles when it was ratified by New Hampshire on June 21, 1788.
The two documents have much in common - they were established by the same people (sometimes literally the same exact people, though mostly just in terms of contemporaries). But they differ more than they do resemble each other, when one looks at the details. Comparing them can give us insight into what the Framers found important in 1781, and what they changed their minds on by 1788.
The following is a comparison, detailing the similarities and differences between the Constitution and the Articles. The topic page for The Articles and the Constitution Explained Page may also be of some interest.
