Conversation so far:
Where did Murray Rothbard attend college?
Murray Rothbard attended Columbia University
What did Murray Rothbard study at Columbia University?
Murray Rothbard received a Bachelor of Arts degree in mathematics
Did Murray Rothbard receive a Masters degree?
Murray Rothbard received Ph.D. in economics
What achievements did Murray Rothbard have during college?
Did Murray Rothbard attend college with anyone significant?
Murray Rothbard attended college with Joseph Dorfman
Why did Murray Rothbard and Joseph Dorfman have a conflict?

Question: What was the subject of his doctoral dissertation?
Self-contained rewrite: What was the subject of Murray Rothbard's doctoral dissertation?