You assume China had a Vault network? Also America by the time of the Great War had overrun most of China, America was winning the Sino-American War. Which would explain why China launched the nukes because it was their only card left to play. They were the spoiler, as in "We can't win, so we will take you down with us!"
America having successfully invaded China, if their was a "vault program" in China. America would have captured and or targeted them with their nukes.
Agreed. Invading America in the first place as an act of desperation. Their resources were running out (like everyone elses) and America had the Oil they needed to stay in power. So they invaded in the hopes they could take the oil and starve America's war machine so America couldn't retake the oil.