Over the past four decades, Afghanistan has witnessed complex transformations rooted largely in deep ethnic and sectarian divisions. The country’s social structure is highly diverse and mosaic in nature; however, the distribution of political power has remained predominantly ethnocentric, hindering the effective participation of major ethnic groups in national decision-making processes. This study, using a descriptive–analytical method, explores the role of ethnicity in weakening the political community and contributing to the collapse of the Afghan state between 1978 and 2021. The findings reveal that subnational and ethnic identities have overshadowed national identity, intensifying mutual distrust, fostering fragile state structures, and perpetuating recurring power struggles. Furthermore, the inability of successive governments to manage ethnic diversity and establish equitable mechanisms for political participation has deepened crises of legitimacy and governance. Consequently, ethnic and sectarian cleavages have not only emerged as major barriers to nation-building and political institutionalization but have also, in conjunction with economic and institutional weaknesses, accelerated state disintegration and prolonged instability.