The Lincoln impersonator answers, "Slavery," followed by a rapid-fire montage of Southern African-American slavery, Communist labor camps, and Nazi concentration camps.
"We shed a lot of blood to stop that in the past, didn't we?" Barber says. "Now look at us. We are all becoming slaves to our government."
From a historical standpoint, Barber's ad does have a few errors. For one thing, Alabama conservatives did not shed a lot of blood to stop slavery -- they shed a lot of blood to perpetuate it, in opposition to a powerful federal government. Indeed, it's quite interesting to see a Southern right-winger putting words into Lincoln's mouth on this subject.
Late Update: As commenters have pointed out (and indeed, a history buff like myself is ashamed to admit he didn't think of it first), Lincoln was a lifelong champion of the traditional Whig policies of "internal improvements" -- that is levying taxes, usually through tariffs, to fund infrastructure projects throughout the country, and incorporating the principle of central banking. In addition to prosecuting the Civil War, Lincoln's administration put all of those policies into effect, as his Republican Party's political coalition was built upon the foundation of the northern Whigs.
Late Late Update: Let's make this whole thing even funnier. Rick Barber, who has declared that the income tax is a tyrannical act that forces Americans to spy on themselves for the government, has invoked the name and image of Abraham Lincoln -- who implemented the first income tax in this country's history, in order to pay for the Civl War.