Simplify the following text for a Grade 15 native English-speaking person.
Original: Diem 's refusal to enter into negotiations with North Vietnam about holding nationwide elections in 1956 , as had been stipulated by the Geneva Conference , would eventually lead to war breaking out again in South Vietnam in 1959 - the Second Indochina War .
Simplified: Diem 's refusal to enter into negotiations with North Vietnam about holding nationwide elections in 1956 , as had been suggested by the Geneva Conference , would eventually lead to war breaking out again in South Vietnam in 1959 - the Second Indochina War .