In this study, we explore the challenges social studies teachers in Japan and South Korea encounter while addressing sensitive and difficult topics essential for fostering inclusive education. As the educational landscape continues to diversify, these educators often find it challenging to incorporate themes such as human rights, multiculturalism, and global citizenship into their curriculum, especially with a traditional emphasis on competency-based citizenship. Utilizing data from the 2018 Teaching and Learning International Survey, we investigate the influence of Teaching in Diverse Environments (TEDE) on Social Studies Teachers’ Attitudes Toward Inclusion (TAI), the mediating role of Global Citizenship Education (GCE) in this relationship, and the potential moderating effect of Teaching Cross-Curricular Skills (TCS) within the educational contexts of Japan and Korea. A significant finding from our research is TEDE’s role in diminishing stereotypes and enhancing diversity awareness among teachers and students alike. We highlight the significance of diverse classroom experiences, engagement in GCE, and the integration of TCS as crucial elements enabling teachers to effectively tackle challenging topics in social studies. Notably, the influence of TAI on GCE, and the significance of TCS, were observed exclusively in Japan, underscoring the need to focus on classroom dynamics and teacher professional development, rather than solely on the cultural, historical, or macro-educational system context.