No, not the problem of war. China and Vietnam's economy development began nearly at the same time. If you want to say the wars killed a lot of Vietnam people and destroyed Vietnam economy, yes, it is the truth. But dont forget China's stupid and cruel class struggle, stupid Great Step Forward, Cultural Revolution, yes, they are not war time, but actually China has never focused on economy since 1990s, and countless Chinese people died during that black period and lost much more than all Vietnam wars put together.
China, Vietnam and even India, they are all carrying on economy reform, but why only China can get a big success? The same between China and Vietnam is they all absorb those forgien investment, especially the investments from Japan. Japan helps China's economy reform just like a kind of reparation and they gave a lot of support whatever on economy or Tech when the pioneering days of reform. But China has difference with Vietnam, because China has a very rich and powerful oversea group and the same blood people come from Taiwam, HK, Singapore and South East Asia .
While Vietnam, to be honest, apart from those people works in restaurants abroad, rarely can find other places that Vietnam can do(just the truth). Those oversea Chinese, Taiwan, HKers. They are the strong engine of China, this is Vietnam or India, they cannot be campared.