Texas purchased almost 140,000 copies of the brand-new textbook that calls slaves "workers."Danny Nicholson/Flickr/Creative Commons

Texas's latest textbook controversy involves a high school edition of publishing giant McGraw-Hill's new World Geography, in which a caption refers to African slaves who were forcibly brought to the Americas as "workers." The company's CEO, David Levin, wrote a letter of apology to his employees Monday.

"In life and business mistakes are made. The first step in correcting them is acknowledging them," Levin wrote. "We made a mistake."

According to the Texas Education Agency, districts in the state bought a combined 138,930 copies of that textbook this school year.

The caption was brought to the public's attention last week, when Roni Dean-Burren, a resident of Texas, posted a photo of the textbook to Facebook. Dean-Burren's son had texted her the photo, along with a note that read, "We was real hard workers wasn't we," and a disappointed-looking emoji.