Pittsburgh boomed after the War of 1812, when factories made iron, glass, and tools. In 1816, it officially became a city. Steamboats on the rivers carried goods far and wide, making trade easy.
Immigrants from Wales, Ireland, and Germany brought skills to build even more factories. By the 1840s, it was one of the biggest cities west of the mountains. A big fire in 1845 burned many buildings, but workers rebuilt stronger.
The Civil War and steel inventions, like Andrew Carnegie's mills in 1875, turned Pittsburgh into the steel capital. Railroads linked it to the world, producing tons of steel by 1910.