[61] After 1916, the Hoovers began living in the United States, maintaining homes in Stanford, California, and Washington, D.C.[62]
Hoover's elder brother Theodore also studied mining engineering at Stanford, and returned there to become dean of the engineering school. In retirement, Theodore bought a large property on the remote north coast of Santa Cruz County. The Theodore J. Hoover Natural Preserve is now part of Big Basin State Park.

World War I and aftermath
Relief in Europe
Further information: Presidency of Woodrow Wilson
Main article: Commission for Relief in Belgium
Hoover with his son Allan (left) and his grandson Andrew (above), 1950
World War I broke out in August 1914, pitting Germany and its allies against France and its allies.  The German plan was a quick victory by marching through neutral Belgium to envelop the French Army east of Paris. That failed but the Germans did control nearly all of Belgium for the entire war.  Hoover and other London-based American businessmen established a committee to organize the return of the roughly 100,000 Americans stranded in Europe. 