What factor significantly influenced U.S. population growth from 1860 to 1890?

The significant influence on U.S. population growth from 1860 to 1890 can be attributed primarily to immigration. During this period, the United States experienced a substantial influx of immigrants from various regions, particularly Europe. These immigrants were drawn to the U.S. for various reasons, including economic opportunities, the promise of land, and the escape from political or social unrest in their home countries.

This wave of immigration led to rapid urbanization and an increase in the labor force, which was particularly vital for supporting the growing industries of the time. Cities expanded, and immigrant communities formed, contributing to the demographic diversity of the nation. The combination of people arriving in large numbers and the opportunities available in America during this industrial expansion created a population surge that was distinct for this historical period.

While industrial development, military expansion, and territorial acquisition also played roles in shaping the United States during that time, the direct impact of immigration on population growth during these years is the most significant factor in understanding demographic changes.