Final answer:
The significant pull factor that drew Chinese immigrants to the U.S. in the mid-1800s was the economic opportunities arising from the Gold Rush and the construction of the Transcontinental Railroad.
Step-by-step explanation:
The pull factor that accounted for much of Chinese immigration to the United States in the mid-1800s was an economic boom in the West. The first wave of Asian immigrants, specifically Chinese, came to the American West for economic opportunities, predominantly due to the California Gold Rush and the construction of the Transcontinental Railroad. Men came to work and send money back to their families in China, engaging in rigorous and often underpaid labor in mining and agriculture.