Slavery wasn't just "used more as a political weapon"--it was one of the primary political and human issues dividing the united States (downcase intentional). The acts of secession were seen as in violation of the Constitution and a detriment to building a United States (upcase intentional). To suggest slavery was merely "used more as a political weapon" reads as if there's an implicit statement that it was not a huge political problem. The facts of history overwhelmingly suggest that it was. There is a reason that long before the civil war, Americans considered themselves to be members of either free states or slave states.
Moreover, there is far more historical evidence to suggest that the war, and not slavery, was "used more as a political weapon" to resolve the divisive issues surrounding slavery and the primacy of the US Constitution. Suggesting that slavery was used as a political weapon falls down when one looks at the post-assassination history, particularly the negotiations between the Johnson administration and the reconstructing state governments in the South. American support for the abolition of slavery had been present since the time of the Constitution. The problem in the intervening 70 years was that most people saw slavery as constitutionally protected, requiring a political solution that would abolish it permanently (e.g., an amendment). The war was, ultimately, the political weapon used to find a solution.
Even as far back as the ratification of the Constitution, these tensions existed. Twenty years prior, in the 1770s, there were already known and notable movements to abolish slavery in the colonies. Lincoln introduced an amendment to a resolution abolishing slavery in DC in 1849. The Compromise of 1850 leaves zero room to suggest that slavery was not an inherently and fundamentally divisive issue for which the Congress was trying to find any peaceful, political way possible to resolve it while mitigating growing tensions. The Kansas-Nebrasks Act of 1854 brought Lincoln back out of what looked like political retirement because he felt it was wrong to leave the slavery question a matter of popular vote in new territories. His opinions on slavery are well-documented, before and during his presidency.
> This declared indifference, but I must think, covert real zeal for the spread of slavery, I cannot but hate. I hate it because of the monstrous injustice of slavery itself...it deprives our republican institutions to taunt us as hypocrites...the real friends of freedom to doubt our sincerity...it forces so many really good men amongst ourselves into an open war with the fundamental principles of civil liberty-criticizing the Declaration of Independence and insisting that there is no right principle of action but self interest.
> The doctrine of self-government is right-absolutely and eternally right-but has no just application as here attempted. Or perhaps I should rather say that whether it has such just application depends on whether a negro is not or is a man. If he is not a man, why in that case, he who is a man may, as a matter of self-government, do just as he pleases with him. But if the negro is a man, is not to that extent, a destruction of self-government, to say that he too shall not govern himself? When the white man governs himself, that is self-government; but when he governs himself, and also governs another man, that is more than self-government-that is despotism. If the negro is a man, why then my ancient faith teaches me that ‘all men are created equal,' and that there can be no moral right in connection with one man's making a slave of another...What I do say is, that no man is good enough to govern another man, without the other's consent.
> Allow all the governed an equal voice in the government, and that and that only is self-government...Near eighty years ago we began by declaring that all men are created equal; but now from that beginning we have run down to the other declaration, that for some men to enslave others is a ‘sacred right of self-government.'...Let us return to the position our fathers gave it...Let us re-adopt the Declaration of Independence. We shall have so saved [the Union], that the succeeding millions of free happy people, the world over, shall rise up, and call us blessed, to the latest generations.
Perhaps close to your cited statement on Lincoln's wanting to keep slavery and the Union, you are mischaracterizing his intent:
> ...Nebraska is urged as a great Union-saving measure. Well I too go for saving the Union. Much as I hate slavery, I would consent to the extension of it rather than see the Union dissolved, just as I would consent to any great evil, to avoid a greater one. Slavery is founded in the selfishness of man's nature-opposition to it is in his love of justice...repeal all past history, you still cannot repeal human nature.
For Lincoln, as with others who sought a political solution, the biggest problem was maintaining fidelity to the Constitution and the Union, while solving what was seen as a national problem:
> You ought rather to appreciate how much the great body of the Northern people do crucify their feelings, in order to maintain their loyalty to the constitution and the Union.
The apologists for the Confederacy who to this day stupidly refer to the Civil War as the War of Northern Aggression, those who try to rewrite the intent of the actors before, during, and after the Civil War--those who attempt to hide behind the statement that the Confederacy seceded to exert and protect States' Rights--willfully ignore history to advance an insidious viewpoint.
Nobody involved, not even Lincoln, disputed that the secession and the resulting Civil War was a matter of States' Rights. More importantly, everyone at the time knew exactly which rights the States were seceeding and fighting to protect.
This is a matter of historical record, not some alleged pro-North viewpoint.
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Now, beyond that, it is a matter of historical record that Lincoln committed constitutionally questionable actions, based on his interpretation of his wartime powers and other factors. That he committed "many constitutional wrongs" is a likely candidate for debate, but can only be discussed if you care to mention what those wrongs were. This article definitely highlights some of them. Arguing that he "increased the size and scope of the federal government" also requires significant explanation of exactly what you mean. Excluding the wartime expansion of budget and federal employees, which dramatically shrunk after his death and the war's end, what specifically are you referring to here?