The subject of urban security offers new causes for reflection related to the modern global geopolitical scenarios. In these context, the traditional meaning of fear is replaced by an innovative form of urban insecurity generated in Europe, in particular, with the terrorist attacks in Paris and Brussels. These attacks have highlighted the possible connection between European suburbs and international terrorism: the threat comes from afar, but it is in these urban areas, such as Saint Denis and Molenbeek, that ferments what we can call the anti- Western humus. French refers to these segregated and degraded suburbs with the phrase "zus", zones urbaines sensibles (sensitive urban areas), or banlieue, whereas English prefers to define them no-go zones. States within State, characterized by social alienation and unemployment. At the beginning of our contribution, through the description of the attacks of the last twelve years, we will try to outline the growing unpredictability and asymmetry of internal and international terrorism. Then, we will focus on the conditions of the European suburbs, as geographic-housing settlements that do not offer opportunities for change or cultural exchange. In addition, we will highlight the alleged links between suburbs and terrorists; among whom, it is also possible to identify radicalized third-generation immigrants. In other words, through figures such as Salah Abdeslaam, an example of the lack of integration into the social context of birth and / or adoption, we will try to understand why the suburbs of those European metropolis most affected by international terrorism are more exposed to radicalization. In this sense, we will try to underline how different migration policies and models have influenced the coexistence between immigrants and indigenous people, leading to the same result: the emergence of suburban areas which have become the symbol of no integration. We will focus on the internal dynamics that characterize Paris and London. Despite of having followed different integration policies, they have been among the most affected cities by terrorist attacks in the last years. We will analyze how those aspects related to the fear and the management of immigration policies have influenced the decisions of Britain and France, leading to different choices about leaving or remaining in the European Union. Considering that closing borders is not a viable option, we will show other possible solutions: in military terms, the change of the defense in the main centers of aggregation of the European cities might drop through the English initiative for Neighbourhood Policing Team or the institution of a European Task Force. In the social sphere, as a way of prevention, we suggest the role of educational institutions, because of its basic function of education and aggregation for young generations, in multicultural contexts very difficult to understand and penetrate.