The United States is a federal republic. What is a federal republic you ask? It is a federation or a union of independent states.

Essentially at the onset of the revolution the 13 colonies were independent of one another. Yes they had economic, cultural, social and political ties but they answered to the English Parliament only, not to one another. For example Massachusetts didn't need Virginia if it required extra money to complete projects or more troops for defense and vice versa. In addition, England up until the end of the 7 Years War (also known as the French and Indian War in America) was pretty lax on their regulation and enforcement of laws in the colonies. This is for several reasons the first being the colonial relationship was an entirely new relationship and something Britain was still working work out. Also during the 17th Century Britain was undergoing major governmental upheaval. This prevented Britain from paying full attention on governing their colonies. The colonies had a lot of leeway when it came to taxes and governing. Nick Bunkers, Empire on the Edge, is a great source on how America came to fight Britain.

I say all of that to press upon you the independent nature of the colonies before the revolution. When the colonies declared independence, yes it was in one voice, but they were hardly united politically. Each state had its own government, tax system, laws etc. After the revolution the Articles of Confederation were implemented to form a quasi-national government. This government was essentially impotent at doing anything a national government should do in its most basic sense. Article 2 of the Articles of Confederation states, "Each state retains its sovereignty, freedom, and independence, and every power, jurisdiction, and right, which is not by this Confederation expressly delegated to the United States, in Congress assembled." As you see it was expressly written that each state retains all of its governing powers and remained supreme over the national government, in addition if we look at Article 3, "The said States hereby severally enter into a firm league of friendship with each other, for their common defense, the security of their liberties, and their mutual and general welfare, binding themselves to assist each other, against all force offered to, or attacks made upon them, or any of them, on account of religion, sovereignty, trade, or any other pretense whatever." The states united in a league of friendship. They were not at this time entering into a union where they were subordinate to the national government. Just to drive home the point, the states had the power to appoint military ranks and to pay for war the states levied the taxes but could not be forced to do so by the national government.

This brings us to the constitution. I'm not going to delve into the constitutional convention etc, it is very interesting and if you want to know more read Carol Berkin's, A Brilliant Solution. However, in order for the constitution to become law the states had to ratify it. Meaning they had to approve and agree to its provisions which firmly placed the national government before the states. Every state admitted into the country had to hold a ratifying convention to approve of the constitution. Indeed even the states that seceded during the Civil War, which included 4 of the original colonies, had to re-ratify the constitution in order to be readmitted back into the union. What does this all mean. It means that the states agree to be apart of the nation. They are saying we are sovereign in our own right but agree under the constitution to subordinate certain powers to the national government. I hope this helps! Let me know if you need further explanation!