In April, 1917, the United States declared war on Germany. In addition to sending troops to fight in Europe, Americans waged war on the language of the enemy at home. German was the second most commonly-spoken language in America, and banning it seemed the way to stop German spies cold. Plus, immigrants had always been encouraged to switch from their mother tongue to English to signal their assimilation and their acceptance of American values. Now speaking English became a badge of patriotism as well, a way to prove that you were not a spy.
The war on language was fought on two fronts, one legal, the other, in the schools. Its impact was immediate and long-lasting. German was the target, but the other “foreign” tongues suffered collateral damage. Immigrant languages in America went into decline, and there was a precipitous drop in the study of foreign languages in US schools as well.
The article goes on to describe in detail how the repercussions of this nativist, isolationist sentiment continue to have a far-reaching impact to the present — not only in terms of the foreign-language competence of native-born Americans, but in encouraging a hostile attitude towards the relationship of foreign languages to the English language and American culture as a whole.