treaties, treatise

Treaties or treaties is the plural of "treaty", meaning an agreement or contract signed by two or more countries--
Our senate has refused to ratify three different treaties in the past year.
Both treaties contain provisions for fishing rights.

Treatise or treatise means a scholarly paper; a formal exposition of a subject, in writing--
His treatise on the social structure of beehives caused a sensation.
He is working on a treatise on artificial intelligence.

Now that you know that, you can say--
"His new treatise will examine all of the treaties the United States Senate has rejected."

Note--the plural of "treatise" is "treatises"--
The professor's desk was covered with the treatises of his graduate students.

Note # 2--the singular form of "treaties" is "treaty"--
One nation has accused the other of violating the terms of the arms treaty.