Conflict appears more often between neighboring states. Adjacency generates interaction opportunities and arguably more willingness to fight. We revisit the nature of the border issue and measure geographical features likely to affect states’ interaction opportunities as well as their willingness to fight. We do so for all on-shore borders from the period 1946–2001. Although each border is unique, a general result shows that the longer the border between two states, the more likely they are to engage in low-intensity conflict. This is particularly so for conflicts active during the Cold War and located in highly populated border regions.