The sea provides defensive depth because waiting until an enemy reaches shore means territory has already been lost. Inadequate national security can also become a constitutional problem when communities provide their own protection, policing, courts, and taxation. In this interpretation, the states' assumption of so many security duties weakened belief in the federal government's importance and became one causal factor behind the American Civil War. Local security institutions can grow into rival centres of political authority. Naval power could therefore be presented as a source of national cohesion as well as coastal defence.
Notable Point · 2:42-5:34
The sea as America's defensive depth
A navy keeps danger away from the coast, while weak external security can push local authorities toward separate policing, finance, and political power.