Urban vulnerability has gained significant importance as a fundamental challenge in the modern era, especially when facing natural disasters and human threats. Civil defense, as a preventive approach, helps reduce urban vulnerability and preserve socio-economic security. This article aims to identify and cluster factors influencing the vulnerability of District 21 in Tehran Metropolis, using a civil defense approach and structural analysis. Theoretical data was collected through documentary methods, and empirical data was gathered using a survey-based Delphi technique. The statistical population consists of 30 experts and specialists in civil defense, selected via judgmental or purposeful sampling. This data was processed using structural cross-impact analysis in MICMAC software. Findings from the overall system environment analysis showed 259 relationships with a value of 3, meaning the key factors have numerous connections and significant influence and susceptibility. Other research results from cross-impact analysis indicate a complex and intertwined distribution of driving forces, characterized by both influence and susceptibility. The clustering system of factors shows a concentration in the dual factors area. Out of 37 studied factors, 13 key obstacles were identified: weakness in crisis management, economic instability, lack of public awareness of civil defense, political and social crises, dilapidation and indefensibility, weakness in urban design, social inequality, vulnerability of economic infrastructures, lack of investment in resilient infrastructures, lack of coordination among institutions, climate change, weakness in management systems, and poor participation culture. These forces play a role of high influence and low susceptibility in the system environment, aiming to reduce urban vulnerability in the studied area.
Extended Abstract:
Introduction
The issue of vulnerability of urban infrastructure and the role of passive defense in dealing with this vulnerability is very important in Iranian cities, especially cities like Tehran. Urban infrastructures, which are part of the country's vital and sensitive infrastructures, are the main target of destruction and damage when faced with the dangers of war and natural disasters. In this situation, it seems necessary to carefully evaluate and investigate the role of passive defense requirements in reducing the vulnerability of urban infrastructures. Considering the vital importance of these infrastructures for the stability and security of the country, any disruption in them can lead to urban paralysis and instability. Therefore, it is necessary to investigate and evaluate the role of passive defense in dealing with risks and reducing the vulnerability of these infrastructures. Due to the advances in technology and new equipment, the use of passive defense methods and tools can be used as an effective strategy in reducing the vulnerability of urban infrastructures.

Methodology
The current research, with a future-research approach, identifies the most important obstacles or challenges affecting the future state of vulnerability in the 21st district of Tehran metropolis with a passive defense approach. In terms of practical purpose, this research is a combination of documentary and survey methods, and in terms of its nature, it is based on the new methods of future research, analytical and exploratory science, which was carried out by using a combination of quantitative and qualitative models. is Documentary study method and empirical data of survey method based on Delphi method have been used in preparation of the studied obstacles. To select the Delphi team, since the goal is not to generalize the results, a judgmental or purposeful sampling method was used. The selection criteria of experts and experts are theoretical mastery, practical experience, willingness and ability to participate in research and access. The important point in determining the number of experts is to ensure the comprehensiveness of different perspectives in the research.
Results and discussion
The results of this article showed that the general distribution pattern of vulnerability in terms of mutual effects analysis, in general, indicates the state of an unstable environmental system in which have a complex and intermediate state in terms of effectiveness and effectiveness. The state of clustering of obstacles is indicative of cluster concentration in the two-way part. Other findings of the research indicate that the vulnerability of the 21st district of Tehran metropolis is influenced by a set of economic, social, managerial and environmental obstacles, each of which somehow affects the resilience of this region. Among the 37 active forces, 13 variables had a greater impact on the future state of realization of the vulnerability of the 21st district of Tehran metropolis with a passive defense approach.

Conclusion
Weakness in crisis management, as one of the key obstacles affecting the vulnerability of the 21st district of Tehran, can have serious consequences when crises occur. This weakness is usually caused by the lack of comprehensive planning and lack of coordination between different institutions, which can lead to delays in responding to emergency situations. As a result, this can lead to increased human casualties and financial losses. To reduce vulnerability, there is a need to strengthen management systems and improve local communities in the field of crisis management. Economic instability as an important factor in the vulnerability of Tehran's 21st district can lead to a decrease in investments and demand in the labor market. This instability, especially in times of crisis, can affect the city's ability to provide essential services and infrastructure.
Funding
The findings, in terms of the overall analysis of the system environment, showed that 259 relationships have the number 3, and this means that the relationships of key obstacles are very large and have great influence.