> There is nothing in the US constitution that actually allows secession
True, but there is nothing that forbids it either explicitly. And I could argue that from the History of the US, of how they were formed, and the Declaration of Independence, Secession is very much considered to be a cultural Right.
Even Lincoln said that:
> Any people, anywhere, being inclined and having the power, have the right to rise up and shake off the existing government, and form a new one that suits them better. This is a most valuable, a most sacred right, a right which we hope and believe is to liberate the world.
This is further observed by foreign observers such as Tocqueville after the US were established:
> The Union was formed by the voluntary agreement of the States; and in uniting together they have not forfeited their nationality, nor have they been reduced to the condition of one and the same people. If one of the States choose to withdraw from the compact, it would be difficult to disprove its right of doing so, and the Federal Government would have no means of maintaining its claims directly either by force or right.