Final answer:
Mexico's largest Pacific port south of the Tropic of Cancer showcases its importance in trade, exemplified by the bustling Port of Manzanillo, and historical significance as the location of the earliest Spanish colonies in the Americas.
Step-by-step explanation:
The country whose largest Pacific port is located just south of the Tropic of Cancer is Mexico. This is exemplified by the Port of Manzanillo, which is one of the largest and busiest ports in the country, dealing with a significant portion of Mexico's imports and exports, such as goods to Canada and importing services from Japan.
Additionally, Mexico's strategic position has made it a crucial location historically, as it was the site where Spain established the first colonies in the Americas.