The topics talked about here are part of a large field called historical linguistics. Wikipedia has good articles on historical linguistics, as well as the comparative method, and the concept of a language family. Take a look to learn more about linguistics! Then, check out specific language families such as Indo-European and Algonquian.

There are two other TED-Ed lessons related to this topic: How languages evolve and How did English evolve? (a lesson that fills in some of the details that we omit here due to the fact that the focus of this lesson was further in the past).

There is still a great deal of debate about Indo-European, most importantly about the location of the homeland. To read more about this debate, there are classic books by Mallory and Renfrew, as well more recent works by Anthony. Then, read these articles by Bouckaert et al. At the same site, watch this movie that shows one hypothesis about how Indo-European languages expanded.

To learn more about the distribution of languages across the world, see LL-map or The Ethnologue. For a specific focus on endangered languages, endangeredlanguages.com provides details, along with many clips and resources. At this site, scroll down to learn how many of the current languages on Earth are expected to be endangered by the turn of the century! If you are interested in seeing which other languages are related to English, visit Multitree: A Digital Library of Language Relationships. This site links languages to families and shows different claims about language relationships.