Without context (and particularly without knowing what "the Lincoln's" first reason supposedly was), it's basically impossible to answer this.
Actually, my understanding was that Lincoln always had precisely one reason for the civil war: to preserve the Union. Everything else is subsumed in that.
to win the civil war
End of Civil War.
The Civil War.
Lee surrendered in the civil war to Abraham lincolns hourse in china
The American Civil War
Copperheads (Anti-war Democrats)
Blockading the Southern ports.
honest Abe is one of them
The Civil War.
The Gettysburg Address
To preserve the Union.
nothing