it has been answered before:

• https://www.reddit.com/r/AskHistorians/comments/17kqhl/how_exactly_did_english_become_the_default/

• https://www.reddit.com/r/AskHistorians/comments/2altdj/when_did_english_become_the_language_that_the/

tl;dr English was replacing French as a result of US influence