No.
The answer to this question can be traced back to the Declaration of Independence, when the Founding Fathers said "...That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, - That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."
It is clear that the Founding Fathers intended a Federalistic (e.g. States' Rights) government-- one in which the Federal government was just that-- only a centerpiece, holdning the country together and binding it only where the States could not.
Therefore, no it is not "illegal" for States to secede from the Union
how could new states enter the union
i think it could be a dozen (12)
Right here .
That could be Kentucky or Missouri, which both had three borders with free-soil states. But they had also stayed in the Union, as 'buffer states' that had voted against joining he Confederacy.
The states that DID NOT secede from the Union was Delaware, Maryland, Kentucky, and Missouri. These four states did not secede from the Union because They were Border states, meaning they were between the Union and the Confederacy.
how could new states enter the union
Possibly
Not legally. During the American Civil War, 1861 - 1865, a group of states tried to leave the Union, (secede ), and were prevented from doing so.
Most Southerners believed that states had freely been created and joined the Union and could freely leave the Union. President Lincoln and the North did not believe this.
In states where civil unions are legally recognized, "civil union partner" (or "partner in civil union") is the legal term for what would otherwise be called a "spouse" (i.e. husband or wife) in a legal marriage.
When a state left the Union it was called secession.
The union of the states
... abolish slavery.
It only released slaves of the Confederate States but not the slaves of the Union States. Only the Union slaves could be freed after the war had ended.
They said that the USA was a voluntary assembly of states, and any of them could quit the Union if they wanted.
Formally known as the Articles of Confederation and Perpetual Union, it was an agreement among the 13 founding states that legally established the United States of America as a confederation of sovereign states and served as its first constitution.
Secession