That is a really nice bit of information communication. Hat's off! I feel like I learned a lot and that always makes me happy. One quibble. At the end it mentions why Mexico's west was of interest to the Spanish, but neglects possibly the most important part - it was where the Spanish galleons from the Philippines first landed after the grueling trip across the Pacific as detailed beautifully in Neal Stephenson's "Ba…
Gradual elevation is certainly easier to build roads across than a cliff, and might be another reason there's less east-west divide in North America.