Preserve means keep, maintain. For example, to "preserve the Union" would mean to keep it from falling apart into independent states.
Lincoln wanted to preserve the union to protect and defend.
President Lincoln's main goal was to reunite the union.
To preserve the Union.
The original goal of the union was to preserve the union at all cost.
Union by trying to preserve it.
they wanted to preserve the union and end slavery.
Abrham Lincoln
To preserve the Union
Both. The Union wanted to preserve the country as a whole; they did not want the United States to split up. The Confederacy, however, wanted to separate from the United States, therefore, splitting up the country. So the Union wanted to destroy the confederacy to preserve the United States.
President Lincoln's main goal was to preserve and restore the Union, which was his central sworn duty as President. Although he also wished very much to see the end of slavery, he only pursued that goal when it aligned with the one of restoring the Union.
The Union fought to try to preserve the country. They fought to preserve the Constitution and the Declaration of Independence. At wartime, both sides considered it an honor to fight for their cause.