Nikolai Aleksandrovich Berdiaev, Semën Frank and other philosophers rejected the idea that the emigration should or even could openly challenge the Soviet regime; they recommended a Vekhist philosophy of inner spiritual development and self-perfection as indispensable preconditions for genuine political change. Post-revolutionary Russia, the ultimate realization of Oswald Spengler's ominous warnings of Europe's collapse, might become the site of its resurrection. Berdiaev noted that in Russia the turn away from the spiritual to the material had reached its apocalyptic conclusion and thus had cleared the way for a spiritual rebirth. The Russian philosophical revival did not end with the "philosophers' steamboats" so much as it underwent an involuntary relocation abroad. The exigency of inner spiritual evolution had a central place in Berdiaev's mature philosophical output. The tasks that Berdiaev assigned the emigration were a religious-spiritual variant on the traditional intelligentsia mission to enlighten and serve.