Final answer:
The democratic republic of Mexico differs from the United States in that it has a more monolithic culture due to a history of intermarriage among different racial groups, whereas the U.S. is more multi-ethnic. Additional disparities exist in political structures and social dynamics.
Step-by-step explanation:
A fundamental difference between the democratic republic of Mexico and that of the United States is the nature of their societal and cultural composition, influenced by their historical development. Mexico, as highlighted by Rodriguez, has become a 'melting pot' with high rates of intermarriage among Europeans (Spaniards), the indigenous population, and Africans, leading to a more cohesive and monolithic culture. The United States, on the other hand, maintains a more multi-ethnic society with distinct racial and cultural identities. Differences are also profound in the political and legal realms, where the U.S. employs a federal republic model with representative democracy, while Mexico has its own unique form of governance affected by its history of division between liberals and conservatives and current socio-political dynamics.