Complex sentence: In 1954, French army surrendered to Viet Minh in the famous Battle of Dien Bien Phu which led to the signature of Geneva Accords in the same year, the theatre was used as a temporary shelter for French civilians immigrated from the North Vietnam.
Split into simpler sentences: In 1954, the French army surrendered to Viet Minh during the Battle of Dien Bien Phu which led to the Geneva Accords in the same year. The theatre was then used as a temporary shelter for French civilians immigrating from the North Vietnam.