Why was Vietnam divided at the 17th parallel in 1954?

In 1954, Vietnam was divided at the 17th parallel as a result of the Geneva Accords, which were negotiated following the French defeat at the Battle of Dien Bien Phu.12

The division was intended to be a temporary military measure rather than a permanent political or territorial boundary. Its primary purposes were to facilitate a cease-fire and to allow for the orderly withdrawal of military forces: the Viet Minh forces were to regroup north of the line, while French and State of Vietnam troops were to remain to the south.3142

The agreement also included a provision for nationwide elections to be held in 1956 to reunify the country under a single government. However, this political reunification never occurred. The United States and the South Vietnamese government, led by Ngo Dinh Diem, refused to sign the Final Declaration of the conference or participate in the proposed elections, leading the 17th parallel to become a de facto political boundary between North and South Vietnam.142