By Samantha DengOn March 22, Britain’s Houses of Parliament was attacked by an assailant, who drove a car through people on Westminster Bridge and then stabbed a police officer. The Britain-born attacker, Khalid Masood, was not the subject of any current investigations. Although he had two convictions before, no prior intelligence showed his intent of a terrorist attack. On March 23, ISIS claimed responsibility for the attack.It is astonishing how Islamic State continues to attract foreign Muslims around the world to join it or fight for it, some of which did not show tendency towards terrorism before. According to Graeme Wood, the fact that Islamic State has territory, which makes it qualified as a caliphate, makes it unique from previous terrorism organization such as al-Qaida. One of the people that Graeme Wood interviewed said that reviving and establishing the caliphate “is a duty upon the Muslims” and pledging oneself to a valid caliph is a requirement for “a fully Islamic life.” Islamic State derives its legitimacy from Koran, the religious text of Islam, and prophecies of Muhammad. Its religious origin may be a source of its strong ability to attract new members.Islamic State’s religious core creates difficulty in combating the terrorist group. The best way seems to be deprive Islamic State of its territory in a short term, which directly deprives its legitimacy. However, anything falling short of that may only result in a greater popularity of Islamic State among foreign Muslims, because the Islamic State continues to fulfill its responsibility as a caliphate to fight against the apostasy and non-Muslims.However, such a way seems to be difficult to achieve. After the recent escalation of military movement of US-led coalition in Syria and Iraq, local leaders argue that the big strike may “increase the popularity of al-Qaeda and Isis”. Such complaint is expectable and this dilemma is something that US has to deal with. Carrying out decisive strike against Islamic State may lead to conflict with other power in Syria, such as Russia and Turkey, but anything else may only result in greater popularity of Islamic State. Sources:https://www.nytimes.com/video/world/europe/100000005005241/isis-claims-london-attack-after-assailant-named.html?rref=collection%2Fsectioncollection%2Fworldhttps://www.ft.com/content/3d607fda-1082-11e7-a88c-50ba212dce4dhttp://blogs.ft.com/the-world/liveblogs/2017-03-23/?ft_site=falcon&desktop=truehttps://www.theatlantic.com/magazine/archive/2015/03/what-isis-really-wants/384980/