This research analyzes the contribution of learning the history of early independence in fostering a philosophical understanding of nationhood. The research questions are: 1) What kinds of philosophical understanding of nationhood are perceived as pro-Islamism and pro-secularism by high school students? 2) How is nationalist behavior expressed as an act of accepting secularism and opposing Islamic fundamentalism by high school students? Moreover, 3) How do factors contribute to high school students' actions and philosophical understanding of nationhood? This research was carried out using qualitative methods. This research involved 34 students enrolled in class XI 6. We researched at SMA 1 Semarang (a High School) in Indonesia. This research analyzed data from memos written by students, class activities, and conversations. Data was analyzed using qualitative content analysis. The findings showed that the nation's pro-Islamist philosophy is reflected in an attitude of fanaticism, difficulty accepting differences, and support for a closed system. A pro-secularism attitude is reflected in accepting differences, moderation, and prioritizing universal values. Accepting secularism and rejecting Islamic fundamentalism is perceived as an attitude of accepting historical agreements, moving away from fanaticism-based conflicts, and preparing for a more democratic future. The philosophical understanding of nationhood is formed by in-depth arguments on socio-political-religious phenomena, acceptance of historical agreements, and hopes for a peaceful future. The findings indicate that future research needs to investigate the teaching of national philosophy in Indonesian history material in different periods or events. They can also be carried out for teaching national philosophy in other places or countries.