Abraham Lincoln's Gettysburg Address has inspired Americans for generations, but consider his jarring remarks in 1862 to a White House audience of free blacks, urging them to leave the U.S. and settle in Central America.

"For the sake of your race, you should sacrifice something of your present comfort for the purpose of being as grand in that respect as the white people," Lincoln said, promoting his idea of colonization: resettling blacks in foreign countries on the belief that whites and blacks could not coexist in the same nation.

Lincoln went on to say that free blacks who envisioned a permanent life in the United States were being "selfish" and he promoted Central America as an ideal location "especially because of the similarity of climate with your native land — thus being suited to your physical condition."

As the nation celebrates the 150th anniversary of Lincoln's first inauguration Friday, a new book by a researcher at George Mason University in Fairfax makes the case that Lincoln was even more committed to colonizing blacks than previously known. The book, "Colonization After Emancipation," is based in part on newly uncovered documents that authors Philip Magness and Sebastian Page found at the British National Archives outside London and in the U.S. National Archives.

In an interview, Magness said he thinks the documents he uncovered reveal Lincoln's complexity.

"It makes his life more interesting, his racial legacy more controversial," said Magness, who is also an adjuct professor at American University.

Lincoln's views about colonization are well known among historians, even if they don't make it into most schoolbooks. Lincoln even referred to colonization in the preliminary Emancipation Proclamation, his September 1862 warning to the South that he would free all slaves in Southern territory if the rebellion continued. Unlike some others, Lincoln always promoted a voluntary colonization, rather than forcing blacks to leave.

But historians differ on whether Lincoln moved away from colonization after he issued the official Emancipation Proclamation on Jan. 1, 1863, or whether he continued to support it.

Magness and Page's book offers evidence that Lincoln continued to support colonization, engaging in secret diplomacy with the British to establish a colony in British Honduras, now Belize.

Among the records found at the British archives is an 1863 order from Lincoln granting a British agent permission to recruit volunteers for a Belize colony.

"He didn't let colonization die off. He became very active in promoting it in the private sphere, through diplomatic channels," Magness said. He surmises that Lincoln grew weary of the controversy that surrounded colonization efforts, which had become enmeshed in scandal and were criticized by many abolitionists.

As late as 1864, Magness found a notation that Lincoln asked the attorney general whether he could continue to receive counsel from James Mitchell, his colonization commissioner, even after Congress had eliminated funding for Mitchell's office.

Illinois' state historian, Tom Schwartz, who is also a research director at the Abraham Lincoln Presidential Library in Springfield, Ill., said that while historians differ, there is ample evidence that Lincoln's views evolved away from colonization in the final two years of the Civil War.

Lincoln gave several speeches referring to the rights blacks had earned as they enlisted in the Union Army, for instance. And presidential secretary John Hay wrote in July 1864 that Lincoln had "sloughed off" colonization.

"Most of the evidence points to the idea that Lincoln is looking at other ways" to resolve the transition from slavery besides colonization at the end of his presidency, Schwartz said.

Lincoln is the not the only president whose views on race relations and slavery were more complex and less idealistic than children's storybook histories suggest. George Washington and Thomas Jefferson were both slaveholders despite misgivings. Washington freed his slaves when he died.

"Washington, because he wanted to keep the union, knew he had to ignore the slavery problem because it would have torn the country apart, said James Rees, director of Washington's Mount Vernon estate.

"It's tempting to wish he had tried. The nation had more chance of dealing with slavery with Washington than with anyone else," Rees said, noting the esteem in which Washington was held in both the North and the South.

Magness said views on Lincoln can be strongly held and often divergent. He noted that people have sought to use Lincoln's legacy to support all manner of political policy agendas since the day he was assassinated. And nobody can claim definitive knowledge of Lincoln's own views, especially on a topic as complex as race relations.

"He never had a chance to complete his vision. Lincoln's racial views were evolving at the time of his death," Magness said.