When reading the Constitution I came across this SECTION. 10.
1 No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold and silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law im- pairing the Obligation of Contracts, or grant any Title of Nobility.
This to me seems to make it apparent the 13 states could not allow any other states to join the union as the constitution would fall under the “ Treaty, Alliance, or Confederation” wording. The articles of confederation had provisions for other states to join but the constitution replaced that right? So how did the other states get the authority to join?