<![CDATA[This study aims to develop a valid, practical, and effective multicultural-based history textbook to enhance a sense of nationalism among high school students in Mataram City and to support the development of contextual, inclusive, and national unity-oriented history teaching materials. The study employed a quantitative approach using the Research and Development (R&D) method, which adapts the ADDIE model comprising Analysis, Design, Development, Implementation, and Evaluation. The field test subjects consisted of 64 10th-grade high school students in Mataram City, with 32 students in the experimental group and 32 in the control group. Research instruments included an expert validation sheet, teacher and student response questionnaires, interviews, observations, a history comprehension test, and an inclusive nationalism scale. Data were analyzed using descriptive statistics, N-gain, paired-samples t-tests, independent-samples t-tests, Cohen’s d, and ANCOVA after conducting tests for normality and homogeneity of variance. The results showed that the product achieved an average validity of 92.80%, categorized as “highly valid,” and a practicality score of 92.00% based on teacher responses and 92.53% based on student responses, both categorized as “highly practical.” Effectiveness tests showed a higher improvement in the experimental group compared to the control group, with a main effect p < 0.001 and a very large effect size (d = 1.585–2.778). The ANCOVA results indicated a strong effect on historical understanding (ηp² = 0.757). Consequently, textbooks that integrate local history, multiple perspectives, source criticism, inquiry, and history projects can serve as effective supplementary teaching materials for strengthening students’ understanding of history as well as fostering inclusive nationalism.]]>
