Terrorism involves using violence against civilians to create fear and force political or social change. Terrorist groups are often organized into cells and carry out bombings, shootings, or kidnappings. They are motivated by a variety of political, religious, or environmental beliefs and seek to undermine the current social order through fear and destruction. While terrorist attacks have increased in recent decades, terrorist groups prefer conventional weapons over weapons of mass destruction due to the difficulty of obtaining such arms and the risk of losing public support through their use. Notable modern examples include the 1995 sarin gas attack in Tokyo by the Aum Shinrikyo cult and the September 11th, 2001 attacks on the World Trade Center and Pentagon by al-Qaeda.