Step 1: Recall who the “purists” are.
A purist is someone who insists on strict adherence to traditional forms, rules, or principles — especially in language, art, or style.
Step 2: Apply this to the context.
In the passage, the purists resist “fusion music,” insisting it violates purity and borders of music. Their opposition is not generational but ideological: defending what they see as the original, uncorrupted essence.
Step 3: Eliminate options.
(A) general ideological conflict → true, but less precise.
(B) younger vs older → not mentioned. ✗
(C) preserving core principles → exactly describes purists’ stance. ✓
(D) marginal groups → irrelevant. ✗
(E) social identity → too sociological, not musical. ✗
Step 4: Conclude.
Therefore, the purists’ war is about preserving fundamental principles.
\[
\boxed{\text{Option (C)}}
\]