If the union was not important then why entice any State to ratify the U.S. Constitution? The U.S. Constitution states the union already existed in its preamble and Article VII states..."The Ratification of the Conventions of nine States, shall be sufficient for the Establishment of this Constitution between the States so ratifying the Same." This proves the union already existed, and for the Constitution to be law it took nine States to approve it- we see here that the minimum number of States, in union, for the Constitution to exist was 70% of the United States. This was not a new union, it was the same union with a new government.
Lincoln pushed the idea that the Federal Government,...i.e. the U.S.Constitution, created the States- created Union, and therefore was supreme over the States. He believe the States were not soveriegn and had no particular rights that superceded the Federal Government.
The States, united, created both governments. They, united, seceded from one government, and formed another- upon approval of those States wishing to change governments. The U.S. Constitution does not have any power without the unity of the States that it governs. This was proven by the secession of several States in 1860-61, that without the power of the people from ALL the States, the Federal Government would run amok- remove, at will, Constitutional rights of individuals and pit State against State.
The Southern States that formed the Confederacy did not secede because they thought the U. S. Constitution was more important than the Union. On the contrary, the Union was very important to the Southern States. When the Union failed- many Southern States left it in order to protect themselves from the evils of an imperfect unity. Their first object was to form a perfect union for themselves.