Previously, EU treaties or laws do not provide for any provision on a state`s ability to voluntarily withdraw from the EU. The absence of such a provision made withdrawal technically difficult, but not impossible.  Legally, there were two interpretations as to whether a state could withdraw. First, that sovereign states have the right to withdraw from their international obligations;  and second, the treaties are for an unlimited period of time, without any provision for withdrawal and without requiring an “ever closer union” – such a commitment to unification is incompatible with unilateral withdrawal. The Vienna Convention on Treaty Law stipulates that a party unilaterally withdraws from a treaty that is silent to secession, there are only two cases where withdrawal is allowed: if all parties recognize an informal right and the situation has changed so radically that a signatory`s obligations have changed radically.  The Withdrawal Act set the period until 21 January 2019 to allow the Government to decide on the way forward if the negotiations did not result in an agreement in principle on both the withdrawal regime and the framework for future relations between the UK and the EU; On the other hand, the future ratification of the withdrawal agreement as a treaty between the UK and the EU depends on the prior adoption of another legislative act of Parliament that approves the final conditions for withdrawal after the conclusion of the current Brexit negotiations. In any event, the Law does not change the two-year article 50 deadline for negotiations, which will end on 29 March 2019 at the latest, if the United Kingdom has not ratified a withdrawal agreement by then or if the negotiating period has been extended.  During the Brexit negotiations in 2017, both sides agreed that trade negotiations could only begin after the UK withdrew, as such negotiations could not take place if the UK still has a veto within the EU.  For this and other reasons, a transition period was set after Brexit day to allow for these negotiations.