See. Among the items:
It may not strike us now as odd that we use "The United States" as a singular noun, but this wasn't always the way everyone spoke. Google N-gram data, which tracks words across Google Books, shows that in the mid-1800s, it was roughly as common to refer to the United States in the singular sense as it was to refer to the United States as a plural group of states that were united. It reveals a profound shift in how Americans think. In the late 19th century, Americans appear to have started thinking of the US as one big actor instead of many smaller ones.