After 13 years of war and an estimated $1 trillion1 in wartime spending, the United States finds itself once again engaged in a deadly struggle with a brutal terrorist group halfway around the world. The violent rise of the Islamic State of Iraq and Syria (ISIS) has shattered the perception that the tide of war is receding. ISIS’ ability to fight and conquer territory and its willingness to commit atrocities, evidenced by multiple beheadings, have alarmed the American people and compelled the U.S. government into action.ISIS, however, represents just the latest threat from Islamic extremism. After the events of 11 September 2001 (9/11) the national debate centered on how best to protect the nation from further attack. Academics and pundits debated endlessly on the proper response to terrorism. In 2002, the United States declared that its primary national security objective was “to disrupt and destroy terrorist organizations of global reach.”2 The U.S. government then undertook its largest reorganization since the dawn of the Cold War and invaded (and reinvaded) two nations as part of the war on terror. After years of war and defense spending, however, terrorist groups are as active and deadly as ever. Questions remain as to how the United States failed to anticipate the rise of ISIS and how to contain the threat.The situation in Iraq, Syria and elsewhere in the Middle East involves complexities far beyond the scope of this analysis. This study does, however, identify a major gap in the current national debate: the lack of historical context and data. Terrorism is a recurring historical phenomenon that predates the 20th century. Hundreds of case studies exist, even in the past 40 years. In fact, one major American think tank has identified at least 648 terrorist groups since 1968.3 Despite the wealth of data, the present discourse continues to overlook the lessons of history.History, of course, does not provide clear-cut answers for today’s challenges. Indeed, every terrorist group is different. However, a study of the phenomenon of terrorism reveals broader trends that can inform the national debate. The historical data support much of the present national discourse and provide warnings about the realities of the current struggle against ISIS—realities for which the United States is unprepared. With its extremely high capacity to fight and to govern, ISIS is as serious a threat to American interests as any terrorist group we have seen. When it comes to such groups, history teaches that:

• The United States cannot waste any time in assisting the Iraqi, Kurdish and Syrian rebel forces to expand their own capacity to fight and govern, since ultimate success, historically, rests upon the local actors to defeat the enemy.
• The United States and its partners must be prepared to engage ISIS for much longer than the national debate has indicated and to defeat the group in such a way as to prevent its reconstitution.
• The United States should incentivize the Iraqi government to engage with the Sunnis and take clearly defined actions to gain their trust. 
• The United States must provide comprehensive military assistance, to include ground, air and sea forces, to combat ISIS in support of Iraqi, Kurdish and Syrian rebel forces.
• The United States must work with its partners to increase divisions within ISIS’ ranks and to alienate it from the local population and other jihadist groups.