The document summarizes five key factors that contributed to the United States becoming the largest industrial country in the world by 1900: 1. Cheap labor from 20 million immigrants who came for jobs and opportunity between 1865-1910. 2. Abundant natural resources such as water, timber, coal, iron and copper in the expanding West. Railroads linked these resources to markets. 3. The growth of railroads, which stimulated economic growth and linked the growing nation. 4. A laissez-faire government policy with low taxes and few regulations that encouraged industry. 5. Important inventions like the telephone, light bulb, and motion picture that improved productivity, transportation and communication.