I saw some silly tea party facebook page about one of the superbowl ads tonight in which the star spangled banner is sung in diffrent languages. As you might guess the comments on that page were straight xenophobic and ignorant; "muh english".
Why do some of these people cling so hard to English? Wouldn't spanish have some claim as an American language as well because of all the Mexican territory acquired after the Mex-Am war? Also weren't Italian and polish majority languages at some point as well?
Why do some of these people cling so hard to English?
This is a modern-day question about people's current opinions. You might want to direct this to /r/AskSocialScience.
As for the rest, the United States of America was formed in 1789 from 13 English colonies. Regardless of what other territories were acquired later, they were acquired by this English-speaking country. It's not about which language is spoken by more people, it's about which language was spoken by the founders of the country and which language was used in its ongoing government.
One observation:
The territory acquired after the Mexican-American War was not very densely populated; it contributed relatively few Spanish-speakers to the American population, and the major territorial addition of the Texas Annexation incorporated a politically dominant (though not necessarily more populous) class of English-speakers.