According to the analysis the questions are consistently asked from NCERT books. NCERT books covers all the topics which are include in the UPSC Civil Services Syllabus. So mostly the toppers preferred these books. For history preparation class 6 to class 12 NCERT books are important for IAS exam. The topics Mentioned here are more important than the others. NCERT Books cannot be ignored for UPSC Exams and a huge portion of UPSC Prelims can be covered from these. However, you still need a few reference books and a newspaper to cover the UPSC Syllabus. Check Unoreads
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