ISIS has a strong affiliation with Al-Qaeda and the history of the 9/11 terrorist attack; The United States is a leading country in the fight against terrorism. The United States' strategy in the war on terrorism is heavily influenced by realist theory. Globally, terrorism is seen not as a simple criminal action but as a war declared against humanity. This may be related to the realist view of anarchy that all aggression is war and the defense against it is the same or simply going to war. Therefore, the United States views ISIS's association with Al-Qaeda as a threat to national security and may launch a preemptive war in response. If fighting terrorism means annihilating ISIS, then the United States should be willing to accept the consequences and financial destruction, which raises the question of morality.