In South Dakota v. Dole, what did the United States Supreme Court hold?

In a 7-to-2 decision, the Court held that Congress, acting indirectly to encourage uniformity in states' drinking ages, was within constitutional bounds. South Dakota v Dole (1987) is a case that came about after a teenager was killed by a drunk driver. This caused Senator Frank Lautenberg of New Jersey to push for legislation establishing a national drinking age of twenty-one.