Does "which" refer to "the salvation of mankind" or does it refer to "mankind"?

Does "which" refer to "the salvation of mankind" or does it refer to "mankind"?
"which is otherwise destined to..."

Therefore the comprehension and acceptance of Spiritualism are essential things for the salvation of mankind, which is otherwise destined to descend lower and lower into a purely utilitarian and selfish view of the universe. The typical materialistic state was prewar Germany, but every other modern state is of the same type if not of the same degree.


"The History of Spiritualism," by Sir Arthur Conan Doyle