Starting with the view that the Sino-Vietnamese fraternal relationship had ceased to be hearty since 2009 due to Beijing's aggressive moves in the South China Sea; thereof, Hanoi had no choice but to move closer the China's rivals and sustain its pace of military modernization efforts, this piece unravels several root causes behind the post-2016 renewal of China-Vietnam ties from the standpoint of geopolitics. In this respect, it also highlights the "tyranny of geography" as the key to understand that any efforts to form cliques with Vietnam will be in vain if any extra-regional power intends to utilize Vietnam to contain China. Even though the revived relationship is likely to moderate and facilitate their bilateral talks over disputed waters, a new challenge in the making - China’s efforts to elude environmental “run-of-the river” practices in the Mekong Basin - appears to another litmus test for China-Vietnam ties.