Complex sentence: While the delegates began to assemble in Geneva from late April, the discussions on Indochina only commenced on May 8,1954; the Viet Minh had achieved their decisive victory over the French Union forces at Dien Bien Phu the previous day.
Split into simpler sentences: While the delegates began to assemble in Geneva from late April, the discussions on Indochina did not begin until May 8,1954. The Viet Minh had achieved their decisive victory over the French Union forces at Dien Bien Phu the previous day.