Final answer:
The colonization efforts of Portugal and Spain in the 15th and 16th centuries played a significant role in determining the distribution of Portuguese and Spanish in South America.
Step-by-step explanation:
The unrelated factor that would ultimately decide where Portuguese would be spoken in South America and where Spanish would be spoken is colonization. The colonization efforts of Portugal and Spain in the 15th and 16th centuries played a significant role in determining the language distribution in South America. Portugal colonized Brazil, resulting in Portuguese being spoken there, while Spain colonized most of the rest of South America, leading to the prevalence of Spanish in those regions.
Learn more about Colonization and language distribution in South America