Then explain why he waited till halfway through the war to free the slaves if slavery was the cause.
Slavery was the foundation for the split of the
slave states from the
free states.
No
free state joined the Confederacy, no
free state cited states rights and seceeded from the Union.
Lincoln was not president when the first
slave states seceeded.
In 1860, Congressman Laurence M. Keitt of South Carolina said, "The anti-slavery party contends that slavery is wrong in itself, and the Government is a consolidated national democracy. We of the South contend that slavery is right, and that this is a confederate Republic of sovereign States."
In 1860 in New Haven Conn, Abraham Lincoln said, "
the question of Slavery is the question, the all absorbing topic of the day. It is true that all of us -- and by that I mean, not the Republican party alone, but the whole American people, here and elsewhere -- all of us wish this question settled -- wish it out of the way. It stands in the way, and prevents the adjustment, and the giving of necessary attention to other questions of national house-keeping."
That is why South Carolina said in
Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union "The General Government, as the common agent, passed laws to carry into effect these stipulations of the States. For many years these laws were executed. But an increasing
hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, and the laws of the General Government have ceased to effect the objects of the Constitution."
So those who seceeded said the cause of the trampling on states rights by the federal government was "an increasing hostility on the part of the non-slaveholding States to the institution of slavery"... not to slaveholding states, but to the insitituion of slavery itself.
Perhaps one could come to the conclusion that since Lincoln and the South Carolina legislature thought slavery was the issue, that just maybe perhaps slavery was the issue.