The association of radical Islamism Ai-Qeada carried out terroristic attacks in the U.S. soil on September 11, 2001. This event has not only caused serious fatalities of almost 3,000 innocent civilians, but also caused severe impacts on U.S. homeland defense. Also, the international community already turned attention to the challenges and threats caused by terrorism because of 9-11 attacking incidents. The purpose of this study is to explore the definitions, basic contents, types, and behavioral patterns of terrorism by conducting the method of documentary analysis. Furthermore, this article aims to establish comprehensive and farther understanding for terrorism through studying the evolution of modern terrorism, recent activities of terrorists, and damages and threats posed by terroristic attacks.