Why do you think Mexico wanted the border at the Nueces River?

they thoguth it would be best suited there for defence

Explanation:

During the Cold War era, President John F. Kennedy invoked the Monroe Doctrine. during the 1962 Cuban Missile Crisis, when he ordered a naval and air quarantine of Cuba after the Soviet Union began building missile-launching sites there.

The Monroe Doctrine was drafted because the U.S. government was worried that European powers would encroach on the U.S. sphere of influence by carving out colonial territories in the Americas.