Conversation so far:
What was his Thích Quảng Đức's religious background?
Thích Quảng Đức's religious background was Mahayana Buddhism.
Was most Thích Quảng Đức's country also buddhist?
The religious composition of Vietnam 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 the Vietnamese buddhists were the majority, then why were they being persecuted?