from my study of 19th Century US hsitory, the only thing that would have been gained was a huge bloc of Republican voters in a party that was in its infancy, which was soon accomplished until after "Redemption" and "voting reforms" beginning at end the of the 19th Century, leaving most of African ancestry disfranchised de facto and de jure.
Here is a small bit of an excellent essay that touches upon Lincoln, colonization and his statements as late as the 1858 debates:
http://www.friesian.com/racism.htm<begin quote>
Jefferson's views that free blacks should return to Africa can easily be held against him, but even Abraham Lincoln believed much the same thing, for much the same reasons. In his debates with Stephen Douglas in 1858, Lincoln was delabored with accusations that, since he was against slavery, he must be for citizenship and equality for freed blacks. Lincoln replied:
"He
shall have no occasion to ever ask it again, for I tell him very frankly that I am not in favor of Negro citizenship....
I will say then, that I am not nor ever have been in favor of bringing about in any way, the social and political equality of the white and black races -- that I am not, nor have ever been in favor of making voters of the Negroes, or jurors, or qualifying them to hold office, or having them marry with white people. I will say in addition that there is a physical difference between the white and black races, which I suppose will forever forbid the two races living together on terms of social and political equality and inasmuch as they cannot so live, that while they do remain together, there must be the position of superior and inferior that I as much as any other man am in favor of having the superior position assigned to the white man...
I have said that separation of the races is the only perfect preventative of amalgamation... Such separation...must be effected by colonization."
Colonization was Lincoln's preference right up until the day that a delegation, consisting of Frederick Douglass and other black leaders, with Emancipation at hand, told him they actually did not want to go back to Africa. When it came right down to it, that was the end of that. Whatever Lincoln's views about citizenship and political equality may have continued to be, the Constitutional issue was settled after his death with the passage of the 14th Amendment, though "equal protection of the law" was never properly enforced after Occupation forces were withdrawn from the South in 1877.
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To me, I am oddly reminded of the fact that Lincoln was never in close physical proximity with any African-Americans, slave or free, until he served in DC in the H. of Reps. and then as President! His anti-slavery credo was common among many of the non-slaveholding caste in the North as well as the South, only the South's view was effectively silenced in the Early Republic by censorship and the growth of the political power of the slave-holding caste in the Old Southwest, which thwarted many of the Jeffersonian/Jacksonian impulses of the Enlightenment and "independence" that were then so commonly enunciated. Lincoln had a lot of the same spirit as these two, seeing the lands across the Ohio as then across the Mississippi as fulfilling the quest for the Jeffersonian ideal. Unfortunately, at the same time, the ability to hold semmingly contradictary ideas or at least to make public statements that indicate that one does is a hallmark of humanity.
Slaveowners saw perfectly well after the first generation actually born in captivity that all of their ideas of physical and intellectual inate inferiority were bogus: they saw African children grow at precisely the same rate physically and mentally as their own white offspring! Yet this did not debunk this myth.
In my graduate work, George M. Frederickson's "Black Image in the White Mind" is the most important simple component of my intellectual development. GMF holds that white people were simultaneously able to claim that Blacks were "passive" and "agressive", "stupid" and "crafty" as well! One is able to substitute "Jews" or "Catholics" or "Arabs" or "the French" or any other group differentiated as "other" to see this concept in action.
Lincoln was an heir of the Revolution, but Washington and Jefferson were its apostles. All three groped as a blind man without a stick on the issue of slavery. Lincoln was not a deep philosopher, by his own definition, simply a country lawyer. But what a great country lawyer he was! {Actually, corporate railroad lawyer might be more apt than country lawyer.) Whether as a war effort or due to some conversion very late in his unfortunately too short life, Lincoln did effect the freedom of the slaves. However, it was the Radical Republican Congress that completed the task he began. There were still slaves in Maryland and Kentucky when Lincoln was assassinated.
Take away Lincoln's halo. He was not a saint, but he was the most single effective US president to date and his efforts to end the war brought about Emancipation and a unified nation from Maine to California. God bles him for that.