Look, I realize this is hard for you, but follow me on this. You're president of a federation of states, half of which are for slavery with the other half tolerating it in other states and even returning escaped slaves to their owners based on law. Sure, there are those totally dedicated to abolishing it, but they are radical, radical few. So radical in fact that to be one could get you killed.
Now then. Powers as great as yourself (Britain and the European monarchies) have been involved in the slave trade but phased it out by methods of compensation, although they still tolerate in many ways in their colonies and sugar plantations in the tropics.
You want to end slavery in your country. Do you do it by the sword, or the pen?
Clearly, the sword would be your choice. It was Lincoln's also. To the tune of a war so horrific, that all the war dead in the wars that your country will fight over the next 150 years and all the wars it fought prior to your war will still not equal to war dead of your five year war to end slavery.
Unfortunately, the Civil War had nothing to do with slavery ending for the sake of ending slavery. It was a botched attempt for the Washington power brokers (Republicans and their big money backers, northern industrialists) to seize power. It was supposed to be a walk in the park. The first major battle was fought with civilians camped out on the hills thinking it was going to be a picnic!!! After the South routed the North in that battle, Stonewall Jackson told Jefferson Davis "Give me 10,000 troops and I'll give you Washington DC."
Davis refused and wrote in his diary that it was the greatest mistake in his life. Lincoln clearly had no idea what he had wrought.
But fine, you back him up, I don't.
Obviously the pen is preferable. But in the U.S. impossible. There were 16 slave states in the U.S., 18 free states. Since there was absolutely no interest among the slave states in ending slavery by any means, compensated or otherwise, the chance of getting an amendment through the Congress was zero. In order to get it through Consitutional convention it would have taken 38 free states. Do the math, that's 64 total states. Lincoln could add, he knew that he could not end slavery. But he could try and halt the expansion. Which is what he advocated and which is what the South saw as threatening. So they rebelled. And they chose war to further their aims. Lincoln waged the war they forced upon him.
But fine, you back him up, I don't.
Facts back up Lincoln better than I can.