what exactly does "preserve the union" mean? and how did president lincoln do this?

Answer 1

That is still under study.

A quote from Shelby Foote, "Prior to the Civil War, people said 'The United States are...', after the war they said "The United States is...'"
When the southern states left the Union, Lincoln had to backtrack and contradict words he had uttered in connection with the Mexican War, when he said that any group had the right to remover themselves from their ruling government and form a new one.

The process of determining which states would have slaves and which would not, brought about the division, the humanitarian aspect of it was of minor importance. But, slavery made for good talking points. For instance, Lincoln pointed out that the South demanded that they be allowed self representation and still insisted that Blacks could not represent themselves. A hopeless contradiction.

As to how Lincoln preserved the Union, he did not. If you get into a detailed study of the Civil War you will find that, as is always the case, those in power were less than perfect, often less than adequate.

The failure of France andEngland to enter the conflict was instrumental in the South loosing. The Confederacy counted on the need for cotton to bring those two powers to her cause, but the year prior to the war was blessed/cursed with huge cotton crop, and there was a surplus in England and in France. They held back until it was obvious that the industrial North woul defeat the largely agricultural South. And that cotton crop had more to do with preserving the union than any other factor.

Your question would take years of research in order to reach an educated opinion, and it would just be one opinion.

Answer 2

You may remember the Civil War. That was fought to preserve the Union.

Answer 3

He went to war with the south to preserve the Union, the south wanted to secede from the Union, so they could continue slavery.

Answer 4

did not aggree with those who would let the south secede including northern governers and border states - not just the secessionists but those who stayed in the union but were willing to part with the south to avoid war. So he preserved and then brought all secessionist states back with the eventual occupation of those states.