What was the name of the document that was considered as the "first constitution" of the United States?

The Articles of Confederation.

Explanation:

They were written and approved in 1777. Their progress was slowed by the common fears of creating a too powerful central government and by extensive land claims by the states. Congress was the last resort body to solve disputes, and the states remained sovereign and free. Congress powers were: to make treaties and alliances, maintain an army and coin money, but it could not regulate trade and levy taxes.