The United States became the largest industrial country in the world by 1900 due to several key factors: 1) Cheap labor from 20 million immigrants who came for jobs and to escape military service or religious persecution; 2) Plenty of natural resources like water, timber, coal, iron and copper; 3) The expansion of railroads which linked markets and stimulated spending on infrastructure; and 4) A laissez-faire government that imposed no regulations and kept taxes low, fueling industrial growth. Inventions like the telephone and light bulb also increased productivity.