A league of friendships and perpetual union refers to what?

Articles of Confederation?

Yes, you're right.

That is correct! A league of friendships and perpetual union is a phrase commonly used to describe the Articles of Confederation. The Articles of Confederation was the first written constitution of the United States, adopted in 1781. It created a loose alliance among the thirteen original states and emphasized the idea of unity and cooperation between the states. However, it had several weaknesses, such as lack of centralized power and difficulty in enforcing laws, which eventually led to the drafting and adoption of the United States Constitution in 1787.