Final answer:
The Santa Fe Trail is the important commercial route to New Mexico that began in 1821 and was a key path for trade and cultural exchange.
Step-by-step explanation:
The trail to New Mexico started in 1821 is Santa Fe Trail, not Oregon Trail, Appalachian Trail, or California Trail. This commercial route was an important connection between Missouri and Santa Fe, Mexico. It facilitated trade and the exchange of goods between the United States and Mexico.
The important commercial route to New Mexico that was started in 1821 is known as the Santa Fe Trail. This trail served as a vital path for commercial and cultural exchange between the American Midwest and the Southwest during the 19th century. It branched off from the original Oregon Trail as part of the expansion into the West, along with other trails like the California and Oregon Trails.