The collapse of the fourth Republic in Afghanistan was a shock. Despite having advanced equipment, the government of this country did not last more than a month against the Taliban attack. Therefore, the purpose of this research is to investigate and explain the domestic causes of the collapse of the Republic in Afghanistan. The main question is which factors played a major role in the collapse of the Republic in Afghanistan? It is assumed that the factors related to the government level in the four political, military, economic and social dimensions played the main role in the collapse of the Republic in Afghanistan. The findings show that political causes (lack of legitimacy of the government, lack of legitimizing ideology, state-nation gap, national identity crisis, political corruption, lack of effective diplomacy); economic causes (bribery and administrative corruption, reduction of investment, capital flight and poverty and unemployment); social causes (discrimination in employment, moral corruption, politicization of identities, lack of social cohesion and brain drain); and military causes (weak leadership due to lack of meritocracy in the army, lack of strategy in war, politicization of the army) were the main factors of the collapse of the republic in Afghanistan.