Which significant contribution did Mexico make to the USA in the 1860s?

In the 1860s, one of the most significant contributions Mexico made to the USA was through the labor provided for the construction of the transcontinental railroad. Many Mexican workers were employed in the grueling and dangerous conditions of laying tracks and building infrastructure across the rugged landscapes of the United States. Their involvement was crucial for completing the railroad, which was a transformative project that connected the eastern and western parts of the country, facilitating commerce, travel, and communication.

This connection played a vital role in the economic development of the United States during this period, enabling the movement of people and goods more efficiently. The labor force that included many Mexican workers was essential for overcoming the significant challenges posed by the diverse geographical terrains.

The other options do not accurately capture the contributions of Mexico during this time. For instance, while public education and skyscrapers were important developments in the USA, they were not specifically a result of contributions from Mexico in the 1860s, nor was the primary nature of Mexican-American relationships based around agricultural exports at that time. Instead, it was the labor for major infrastructure projects, like the transcontinental railroad, that stands out as a significant contribution during that era.