What were the reasons that made Lincoln abolish slavery? Was it 'just' an act of humanity or did he somehow benefit from abolition economically or socially? Has it ever been suggested that he did because black slaves were needed to serve in the army?

You will find full details of this at:

http://www.spartacus.schoolnet.co.uk/USASproclamation.htm

Lincoln was originally against the use of slaves as soldiers. See

http://www.spartacus.schoolnet.co.uk/USACWcolored.htm

http://www.spartacus.schoolnet.co.uk/USACWenrollment.htm

For a full account of the long-term impact of these measures see:

http://www.spartacus.schoolnet.co.uk/USASreconstruction.htm

See also the long-erm impact on black civil rights here:

http://www.spartacus.schoolnet.co.uk/USAcivilrights.htm