Many contemporary states and historic political entities walled their borders stressing the idea that these barriers would protect their homelands from external threats and thus, achieve security. Although this security argument has prevailed, the political science literature fails to offer a systematic empirical examination of the relationship between barriers and cross-border threats. This research attempts to bridge this gap by answering the question: What are the actual security outcomes of physical barriers on borders? And thus, under what conditions do barriers succeed/fail to achieve security? This paper posits that, in some cases, building barriers on borders to stop non-state actors’ attacks escalate conflict. It demonstrates that when militants have supply institutions, they will manage to increase their attacks and shift to new tactics despite the barrier. It also studies the Israeli Gaza Strip Fence and offers an analysis based on patterns of the relationships between features of the barrier and the Gaza attacks. these patterns are derived from a quantitative dataset built by the researcher and are also supplemented by qualitative data about the case. / text