What race means and what purported characteristics constitute members of a racial group have changed according to time and space.
For a historian, the most important dimension here would be time—however things may be now, they most likely weren’t that way in the past and they almost certainly won’t be the way they are now in the future.
Here’s one example:
Someone who might seem obviously “white” to us in the United States today, like an Italian or someone from Ireland, often would have been considered a different and non-white “race” in the 1800s.
How such groups of people came to be seen as white and to see themselves as white isn’t a biological question, but a historical one.
In addition, a person or group’s race (how they’re seen in the eyes of the law as opposed to their lived experiences) is also often situational.
Another example: the history of Mexican immigrants and Mexican Americans.
The U.S. government saw virtually all of them as “white” and often treated them accordingly in court and at the ballot box when the U.S. conquered much of Mexico in the 1840s.
But most Anglo-Americans and local officials saw them as a different race, not white, and increasingly subjected them to discrimination and often segregation.
As a consequence, a significant share of Mexican Americans have come to see themselves as not white, but members of some other racial group (although they often disagree on what to call that group).
—John Bezis-Selfa, associate professor of history