but others did not. Some owners reneged on their promises to free them after their service in the military. Some African American descendants of Revolutionary war veterans have documented their lineage. Professor Henry Louis Gates and Judge Lawrence W. Pierce, as examples, have joined the Sons of the American Revolution based on documenting male lines of ancestors who served. In the first two decades following the Revolution, most northern states abolished slavery, some by a gradual method others such as Vermont and Massachusetts did so during the Revolutionary period. Northern states abolished slavery by law or in their new constitutions. By 1810, about 75 percent of all African Americans in the North were free. By 1840, virtually all African Americans in the North were either free or living in free state jurisdiction. Although southern state legislatures maintained the institution of slavery, in the Upper South, especially, numerous slaveholders were inspired by revolutionary ideals to free the people they had enslaved. In addition, in this period Methodist, Baptist and Quaker preachers also urged manumission. The proportion of free Black people in the Upper South increased markedly, from less than 1 percent of all Black people to more than 10 percent, even as the number of enslaved people was increasing overall. More than half of the number of free Black people in the United States were concentrated in the Upper South. In Delaware, nearly 75 percent of Black people were free by 1810. This was also a result of a changing economy, as many planters had been converting from labor-intensive tobacco to mixed commodity crops, with less need for intensive labor. After that period, few enslaved people were granted freedom. The invention of the cotton gin made cultivation of short-staple cotton profitable, and the Deep South was developed for this product. This drove up the demand for labor from people who were enslaved in that developing area, creating a demand for more than one million people to be enslaved to be transported to the Deep South in the domestic slave trade. In popular culture The 2000 film, The Patriot, features an African American character named Occam (played by Jay Arlen Jones). He is an enslaved man who fights in the war in place of his master. After serving a year in the Continental Army, he becomes a free man and continues to serve with the militia until the end of the war.