Since the U.S. and its allies attacks on Afghanistan and Iraq which lead to dissolving their regimes, the questions surrounding the legitimacy of these attacks is still under consideration. International Lawyers specially those from developing countries believe that the legal basis of the use of force against these countries in the name of “American Leadership in cooperation on terrorism combat” is in contradiction to article 4(2) of the U.N. charter and specially the fundamental principle of prohibition on the use of force. On the other side, many of the western theoreticians like those of American neo-conservatives, british governors and also coalition forces involved in this attacks are convinced that the right of self-defense would justify the use of force against Afghanistan and carrying out a pre-emptive strike in self-defense against Iraq for its stores of weapons of mass destruction as a dictatorship regime. Given this views which are in accordance with the principles of morality, the author considers that clear terms must be required to authorise the use of force on a international legal basis.