Taking into account the statement above: "The American sociologist who focused on social theory in the 1940s, developing detailed models of how society harmoniously works together was"
The answer is: Talcott parsons.
Explanation: Talcott Parsons was an American sociologist of a classical tradition, he is well known for a social action theory and structural funcionalismo that he created. Also, Parsons is actually considered one of the most influential figures in sociology in the 20th century.
Hope this helps.