who is given the power to admit new states
Admission to the Union The Admission to the Union Clause of the United States Constitution, oftentimes called the New States Clause, and found at Article IV, Section 3, Clause 1, authorizes the Congress to admit new states into the United States beyond the thirteen already in existence at the time the Constitution went into effect.
State cessions In the end, most of the trans-Appalachian land claims were ceded to the Federal government between 1781 and 1787; New York, New Hampshire, and the hitherto unrecognized Vermont government resolved their squabbles by 1791, and Kentucky was separated from Virginia and made into a new state in 1792. The cessions were not entirely selfless—in some cases the cessions were made in exchange for federal assumption of the states' Revolutionary War debts—but the states' reasonably graceful cessions of their often-conflicting claims prevented early, perhaps catastrophic, rifts among the states of the young Republic, and assuaged the fears of the "landless" states enough to convince them to ratify the new United States Constitution. The cessions also set the stage for the settlement of the Upper Midwest and the expansion of the U.S. into the center of the North American continent, and also established the pattern by which land newly acquired by the United States would be organized into new states rather than attached to old ones.