By 1900, inanimate prime movers supply about half of all mechanical energy: coal-fired steam engines make the greatest contribution, followed by better-designed waterwheels and new water turbines (first introduced during the 1830s), windmills and brand-new steam turbines (since the late 1880s), and internal combustion engines (gasoline-fueled, also

as some past setbacks indicate, these technical advances do not make continued progress inevitable: most notably, the first half of the 20th century saw a significant retreat from economic globalization and hence also from the accompanying international movement of people. The reasons for this retreat are obvious, as the decades were marked by an u

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