Most common second language
By looking at the second languages spoken around the United States, we can see its immigrant history and changing demographics. For example, many Germans moved into the United States decades ago and that can still be seen in the middle area of the map. If this map included Spanish, it would probably look a lot different.
There used to not be a large population of people from Asia living across the States, but that has changed over recent decades. Now there are thriving Korean, Vietnamese, and Filipino populations just to name a few. Fascinating how time can change so much and change the face of a nation.