Based on the written words and such of those who conspired with John Wilkes Booth, it was simply because it was a way to strike back at the North, the South having lost the war. (edit: there were three assassinations planned that day, the VP and other other guy. One resulted in a severe wounding, but for the 3rd, the guy chickened out)

Lincoln was only going to prohibit slavery in the new territories, at which point the South would be demographically overwhelmed by free states within a decade or so. They would soon lose power in the Senate and House as those states took their seats, and before long, slavery would have been ended as the South would be a minority. The South saw this coming, and pre-emptively seceded.

Lincoln was going to move forward with shipping the slaves back to Africa, but my understanding is that Fredrick Douglas convinced him not to. I'd love to know more, if someone can share.

Based on the written words and such of those who conspired with John Wilkes Booth, it was simply because it was a way to strike back at the North, the South having lost the war.

Lincoln was only going to prohibit slavery in the new territories, at which point the South would be demographically overwhelmed by free states within a decade or so. They would soon lose power in the Senate and House as those states took their seats, and before long, slavery would have been ended as the South would be a minority. The South saw this coming, and pre-emptively seceded.

Lincoln was going to move forward with shipping the slaves back to Africa, but my understanding is that Fredrick Douglas convinced him not to. I'd love to know more, if someone can share.