Final answer:
The most critical border for Mexico to protect is the U.S.-Mexico border, with shifting entry points due to fortified fencing and additional patrol agents. The journey for undocumented migrants has become more dangerous and less visible to residential populations and humanitarian groups.
Step-by-step explanation:
The most critical border for Mexico to protect is the U.S.-Mexico border. Due to the heavily fortified fencing and additional patrol agents in urban areas like Tucson and El Paso, undocumented migrants have shifted their entry points to more hostile terrains, such as the Sonoran Desert region of Arizona. This has made the journey more dangerous and less visible to residential populations and humanitarian groups, with threats including extreme weather, dehydration, bandits, and wild animals.
Learn more about Mexico's critical border to protect