Final answer:
The primary purpose of President Lamar in sending the Santa Fe Expedition was to take control of trade routes in New Mexico and capture Santa Fe.
Step-by-step explanation:
The primary purpose of President Lamar in sending the Santa Fe Expedition was to take control of trade routes in New Mexico and capture Santa Fe. This was part of the larger goal of expanding American influence and power in the western lands. The expedition was intended to assert American control over the region and secure advantageous trade routes.