Book excerpt: This paper examines how external military threats influence the distribution of population across cities. We argue that such threats reduce government investment, and thus population growth, in cities, particularly in non-democratic countries where governments have broad discretion in how investments are allocated. To test these hypotheses, we construct a measure of external military threat that varies both across cities within the same country and over time and examine its relationship with the growth of a set of large cities over the period 1950-2015. Results from models of city population growth incorporating both city and country-year fixed effects imply that external military threats are associated with slower city growth in non-democracies, but not democracies. Back-of-the-envelope calculations using our baseline estimates imply that post-1950 military threats had resulted in an average increase in population concentration among large cities of approximately 36% by 2015.