Why is the US called Mosaic?

At the turn of the twentieth century, when the USA enjoyed the influx of many immigrants from Europe, people from diverse backgrounds had to learn to get along under the rule of common law while celebrating shared ideals. The simile that emerged then was America as a "melting pot," wherein all the various elements would be blended into one strong alloy. After the civil rights movements during the last half of that century, and after the self-assertion of indigenous peoples around the world, there is more emphasis on retaining cultural identities while being a unified people. The simile of a "mosaic" refers to the beauty of a mural composed of disparate pieces of differently colored tiles.