Continuity mistake: When Lincoln is hacking down the tree, he manages to chop a big part of it, but when he gives the final blow, before the tree sort of explodes, there is not a single scratch on it.
Continuity mistake: While Henry is talking to Abe in the bar after some time of training, we can see that his face has healed. However, in the next scene where he shows Abe the vampire targets, his face is as beat up as before.
Continuity mistake: When Will and Abe are discussing sending more troops, Will is wearing glasses, but when he says "If you do this there is no turning back Abe" there is as side shot and he is no longer wearing glasses, then the shot switches to frontal and there they are again.
Continuity mistake: When Abraham Lincoln picks up the pocket watch left in Willie's room, he opens it, but in the next shot it's closed.
Continuity mistake: When Jack Barts is lying on the ground, right before Abe kills him, his right hand is empty. When he is lying in the casket and Adam opens his hand, there is Abe's pocket watch.
Continuity mistake: As Abraham ends his speech on stage near the end of the movie one of the men behind him puts his hat on twice - once in the camera shot behind, and again in the camera shot from the front. (01:35:10)
Continuity mistake: In the final fight scene atop the train, Lincoln's African American colleague Will is attacked by the head vampire and is knocked backward over the side of the boxcar. He is seen with his feet nearly over the edge and Abe is seen 7-10' away, lying on the forward end of the car, facing him. In the next shot, Will continues his backward fall and Abe's arm appears over the edge of the roof, grabbing Will's leg. There's no way Abe could have risen from his position atop the car and covered the considerable distance in time to reach down and save Will.
Answer: Adam wanted to turn the whole nation into vampires. And as head vampire, he would be the leader. Part of the plot line was vampires feed on slaves, so Adam wanted to keep slavery legal. During the course of the Civil War, Adam conspired with Jefferson Davis to send vampires to the front line to help with the war for the South, in return for claims to the North for his clan (although he would probably turn on the South afterwards).
Bishop73