Simplify the following text for a Grade 9 native English-speaking person.
Original: However , feeling he could not pursue macroeconomics ( his main research interest ) at RAND ( which focused on defense work ) , Phelps decided to return to the academic world .
Simplified: His main interest was macroeconomics , but RAND focused on defense work so Phelps decided to return to the his studies the next year , 1960 .