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After the International Court of Justice ruled that Kosovo’s declaration of independence was not prohibited by international law, I expected Serbs to react with anger. In truth, the reaction was one of indifference. There were no protests in Belgrade or histrionics by Serbian politicians.

The muted reaction was appropriate. International lawyers agree that last week’s decision is mostly notable for what it doesn’t do. The World Court purposely sidestepped difficult questions such as whether the declaration brought about Kosovo’s secession from Serbia and whether nations such as Canada and the United States were legally justified in recognizing an independent Kosovo. The court ruled only that declarations of...