The cheap, strong alloy of iron and carbon that the Bessemer converter made suddenly abundant in the 1850s — whose mass production built the railways, skyscrapers, warships, and reinforced concrete that shaped the modern world, and whose geography of dominance ran from Britain and America through Japan and South Korea to the overwhelming Chinese supremacy of the 21st century.
In 1856, a British engineer named Henry Bessemer discovered he could blow cold air through molten pig iron and, in twenty minutes, burn off the carbon that made iron brittle. He had made cheap steel in industrial quantities for the first time in history. Within fifty years, that discovery reordered the built world: railways spanned continents, bridges crossed wide rivers on slender arches, skyscrapers rose thirty stories in Manhattan, and warships grew large enough to decide the fate of empires. Steel did not merely replace iron. It made things possible that iron had never allowed.