Simplify the following text for a Grade 8 native English-speaking person.
Original: The Tehran Conference ( codenamed Eureka ) was the meeting of Joseph Stalin , Franklin D. Roosevelt and Winston Churchill between November 28 and December 1 , 1943 , most of which was held at the Soviet Embassy in Tehran , Iran .
Simplified: Tehran was the site of the Tehran Conference in 1943 , attended by U.S. President Franklin D. Roosevelt , British Prime Minister Winston Churchill , and Soviet Premier Joseph Stalin .