Complex sentence: The time-honored Confucian philosophy behind the traditional mandarin ethic, although then still prevalent in Vietnam and elsewhere, had been challenged in East Asia, methodically and decisively, since the arrival of western culture.
Split into simpler sentences: The time-honored Confucian philosophy (Vietnamese: "Nho Giao") behind the traditional mandarin ethic, remains in Vietnamese culture and elsewhere. Yet it had been challenged in East Asia, methodically and decisively, since the arrival of western culture.