Black migration from Mexico

Rico's friend Kema (she of the on-line Slavery Museum) sends this article by Henry Louis Gates and Meaghan E.H. Siekman, Ph.D., a researcher from the New England Historic Genealogical Society, from The Root:

Dear Professor Gates:I wonder if my ancestors went the wrong way in their search for land sometime between the mid-1840s and early 1850s. They were black, and they went from Mexico to Natchez, Mississippi during slavery. Why?
My great-great-great-grandfather Thomas Hinyard (or Henyard) was born about 1833. His sister Milly Hinyard McFarland was born in 1837, and his brother Edward (Ned) Hinyard was born in 1840. Slavery had already been banned in Mexico, so why did they leave? I ruled out the possibility that it was in search of their parents, because they, too, were born in Mexico.
Were Thomas, Milly, and Ned part of the seventy-five thousand Mexican nationals granted American citizenship during the time of the Mexican-American War? If so, where can I find resources for this period that may contain clues as to how they were able to stay together and why their journey took place during slavery?
Records indicated that my great-great-great-grandfather Thomas and his brother Edward joined and were active soldiers during the Civil War in the 58th Infantry Regiment Company I, U.S. Colored Troops, in Natchez, Mississippi, and that both had deserted.
The 1900 census indicates that Thomas Hinyard was married circa 1852 to my great-great-great-grandmother Rosanna Prater in Woodville, Mississippi. The three siblings are still all together in the 1870 and 1880 Wilkinson County census. Neither he nor his siblings are on the 1860 census as free people.                                     Eleanor Malden 

As Professor Gates has noted in a previous article, thousands of enslaved Africans were shipped to Mexico. By 1810 that country had over six hundred thousand free blacks, comprising ten percent of the total population. They even had a black president, Vincente Guerrero, in 1829!
It’s a strong possibility that your ancestor Thomas Hinyard and his two younger siblings were born in a location that was in dispute between the United States and Mexico, which may explain why they claimed to have been born in Mexico in the documentation you found and sent to us.
In the span of thirty years, the same land between Mexico and western Texas changed governance four times. Spain lost control to the Mexican government following the Mexican War for Independence in 1821. The region then became part of the Republic of Texas, established 2 March 1836, as an independent sovereign nation that existed until 16 February 1846, when it was annexed by the United States.
The boundary between Texas and Mexico was in dispute for the entire existence of the Republic of Texas. These tensions continued after Texas was annexed as a state and became an impetus to the Mexican-American War from 1846 to 1848. The Texas GenWeb Project includes county formation maps from 1836 to 1930, which help to visualize these areas in dispute and how boundaries for each county changed over time.
If your ancestors were free blacks in the disputed lands between Mexico and Texas, changing boundaries and governments also meant change in law relating to their free status. The Texas State Historical Association has an article on free blacks in Texas, which provides an overview of the changes in laws as the region shifted from Mexico to the Republic of Texas to the United States. It notes that after the Mexican War of Independence in 1821, and prior to Texas independence in 1836, many free blacks moved to Texas for the opportunity to have full rights of citizenship under Mexican law.
The Republic of Texas, however, restricted the rights of free blacks. Permanent residence of free blacks in the Republic of Texas required approval of the Congress of the Republic of Texas and, even if residency was granted, free blacks lost citizenship and restricted property rights. The article notes that “a stricter law passed in 1840, which gave free blacks two years to leave Texas or risk being sold into slavery, was effectively postponed by President Sam Houston.”
It is possible that even the threat of this could have encouraged people such as your ancestors to leave the region. Restrictions only worsened after annexation to the United States, all of which could have encouraged your ancestors to migrate elsewhere.
There is also the possibility that your ancestors were slaves in the disputed region between Mexico and Texas. Among the tensions that led to Texas independence were slave-owning Anglo settlers angered by laws prohibiting slavery in the region. Alwyn Barr in Black Texans: A History of African Americans in Texas, 1528-1995, notes that some slaveholders tried to circumvent the law by making their slaves indentured servants with long terms. If your ancestors had been slaves prior to their service in the Civil War, it may also be one reason they were not enumerated in the 1850 or 1860 U.S. census.
With these two scenarios in mind, we searched for more information on Thomas Hinyard. We located a Thomas Hinyard on an 1867 voter-registration list that recorded his residence as Falls County, Texas. Following the Civil War, the Reconstruction Act required that all eligible citizens, both black and white, register to vote. This record does not indicate this Thomas Hinyard’s race, but it does indicate that someone with your ancestor’s name was registered to vote in Falls County, Texas in 1867.
From the service records you located, you know that your Thomas Hinyard enlisted in the 58th Infantry Regiment Company, I, U.S. Colored Troops in Natchez, Mississippi, in 1865, and that he had deserted. Either your Thomas Hinyard went to Texas following his service or this is a record for another Thomas Hinyard who is possibly related to your Thomas Hinyard (since the surname was rare in this region during this time).
It also can be beneficial to conduct broader searches of your ancestor’s surname. Individuals with the same surname, regardless of their race, may indicate some kind of relationship to your Thomas Hinyard.
During our search, we also located the death certificate for an R. Hinyard in San Saba County, Texas, who died 15 June 1906. The reason we noted this record is that according to the record, R. Hinyard was born in Mississippi, making him another Hinyard with ties to both Mississippi and Texas.
The race of R. Hinyard was recorded as white. This may open the possibility that R. Hinyard or his family could have been the former slave owners of your Thomas Hinyard, which could explain his movement back to Mississippi. Even if your Thomas Hinyard’s parents were also born in Mexico, perhaps they had other family members still in Mississippi. Researching further into the life of R. Hinyard may reveal more about your Hinyard family or present a reason why they moved from Mexico to Mississippi.
You may want to also examine the collections at the Texas State Archives that may aid you in your search. The Texas State Archives hold documents from a number of periods of Texas history, namely Spanish Texas, 1731-1820; Mexican Texas, 1821-36; the Republic of Texas, 1836-45; and the state of Texas, 1846-present. If your ancestors were born in what is now the state of Texas, there may be collections to help you understand their movements. 

Henry Louis Gates Jr. is the Alphonse Fletcher University Professor and founding director of the Hutchins Center for African and African American Research at Harvard University. He is also co-founder of The Root. Follow him on Twitter and Facebook.
Send your questions about tracing your own roots to TracingYourRoots@theroot.com.
This answer was provided in consultation with Meaghan E.H. Siekman, Ph.D., a researcher from the New England Historic Genealogical Society. Founded in 1845, NEHGS is the country’s leading nonprofit resource for family history research. Its website, AmericanAncestors.org, contains more than three hundred million searchable records for research in New England, New York, and beyond. With the leading experts in the field, NEHGS staff can provide assistance and guidance for questions in most research areas. They can also be hired to conduct research on your family.

Rico says this kind of information is invaluable for those who care about their ancestors...