The truth is Lao, Thai and Viet originally came from southeastern China. Lao and Thai originally were from the same group of people and shared the same bloodline. The Viet were a separate group distinct from Lao and Thai. Now Lao and Thai have been each mixed with other ethnic groups, as have been the Viet.
Lao and Viet ເປັນອ້າຍນ້ອງກັນ? No, it's not the truth and it's just a political maneuver. Say that to the real Viet, they may smile in front of you but they will laugh behind your back. The Viet think they are stronger and more intelligent than the Lao. In reality, normal Lao people don't care about the Viet, as do the normal Viet about the Lao.