Conversation so far:
What was his religious background?
Buddhist.
Was most of the country also buddhist?
the religious composition at the time estimated the Buddhist majority to be between 70 and 90 percent.

Question: If they were the majority, then why were they being persecuted?
Self-contained rewrite: If Buddhists were the majority in Thích Quảng Đức's country, then why were they being persecuted?