Jemaah Islamiya (JI) is a Southeast Asian terror organization linked to Al-Qaeda, whose goal is to create an Islamic state comprising Indonesia, Malaysia, Singapore, the southern Philippines, and southern Thailand. While the JI was officially established in the 1990's, its roots go back to "Dar al-Islam" (DAI), an extremist group which fought in the Indonesian struggle for independence and later sent dozens of Indonesian activists to train and fight in the Afghan war. Some of those activists, first and foremost Radwan Issam al-Din (AKA Hambali) were the ones who later established the organization.
The JI was involved in some of the deadliest terror attacks and plots to hit South East Asia, most of them tied to Al-Qaeda as well. Among those: the October 2002 bombings in Bali (202 people dead), the August 2003 Marriott hotel bombings in Jakarta (12 people dead), A late 2001 plot to conduct simultaneous attacks on several western targets in Singapore and another plot to conduct a second wave of 9/11 style operation in south East Asia.
The JI lost some of its key figures in the last few years, starting with Hambali (arrested in August 2003) and continuing with a long list of arrests and killings of activists by the local authorities. These developments were reflected in a sharp decrease of JI's operational capabilities, as well as its target selection, as the organization refocused on local targets instead of international ones. Nevertheless, the strict infrastructure of JI has already helped the organization to regroup in the past, and therefore the JI continues to pose the biggest terror threat in South East Asia.