The correct answer is - The Spanish established their language when they colonized the territories.
During the period of the great discoveries the Spanish managed to occupy most of what is now South America. They implemented their language, culture, and laws, very often with using force and violence because lots of the native people were not willing to give up on their own culture, language, and way of life. The Spanish managed to prevail, and ruled for long enough that the Spanish language becomes the dominant language in nine South American countries.