Opinion of the Court
As New York acknowledges, however, many of those pre-1953 compacts concerned boundaries and water-rights allocation. See Brief for New York 3–4, 30; Tr. of Oral Arg. 30, 33. Those compacts, as we have explained, are not governed by the default contract-law rule authorizing unilateral withdrawal. New York offers no persuasive evidence that the background understanding of withdrawal from boundary and water-rights compacts also applied to compacts that exclusively call for ongoing performance on an indefinite basis by an interstate agency. Indeed, just three years before the Compact here was formed, the United States explained to this Court that a compacting State could unilaterally withdraw from a compact that was silent as to withdrawal and that required an ongoing and indefinite exercise of sovereign authority. See Brief for United States in West Virginia ex rel. Dyer v. Sims, O. T. 1950, No. 147, pp. 23–24, 26–27. In addition, New York overlooks that some compacts, including one formed three years before this Compact, expressly prohibited unilateral withdrawal. See Snake River Compact, Art. XII, 64 Stat. 33; see also, e.g., Goose Lake Basin Compact, Arts. V, VII(B), 98 Stat. 292 (1984). That language would have been unnecessary if New York were correct about the pre-1953 practice.
In short, New York identifies no clear historical practice in support of its view that compacts calling for ongoing and indefinite performance and that were silent on withdrawal were understood as of 1953 to prohibit unilateral withdrawal.
Second, New York invokes international treaty law. According to New York, international law generally prohibits a signatory nation’s unilateral withdrawal from a treaty absent express language otherwise. But to the extent that international treaty practice is relevant here, it is equivocal. Scholars have “long debated” whether nations may unilaterally withdraw from treaties that do not
