On the banks of the Rufiji River, Tanzania has completed a decade-defining act of infrastructure — a 2,115-megawatt hydropower station named for the nation's founding father, built at a cost of $2.1 billion and already supplying nearly half the country's electricity. The Julius Nyerere Hydropower Project arrives at a moment when demand is outpacing supply and when the promise of affordable, abundant energy could rewrite the economics of an entire region. It is a reminder that the most consequential decisions a society makes are often not political but physical — the choice to build, to connect