What was a primary reason for the under-population of Mexico's northern territories?

The primary reason for the under-population of Mexico's northern territories can be attributed to the lack of motivation among people to relocate to those areas. In the 19th century, the northern territories were often remote, sparsely populated, and lacked the developed infrastructure and opportunities that were available in more populous regions. This made the prospect of moving there less attractive to individuals and families seeking better livelihoods.

While certain factors such as the economy or military presence might suggest some level of appeal or safety, the reality was that many people were deterred by the challenges of harsh living conditions, limited resources, and the difficulties associated with relocating to a frontier region. The combination of these factors contributed to a general reluctance to move into these territories, reinforcing the notion that motivation was a crucial barrier to increased population in Mexico's northern areas.