ATHENS—Greece ratified a U.S.-backed deal with Macedonia that aims to help stabilize the Balkan region, but which is roiling Greece’s society and polarizing its political scene.

The agreement, which renames the Balkan country as North Macedonia and lifts Greece’s veto on its neighbor joining the European Union and the North Atlantic Treaty Organization, was passed on Friday by a majority of three lawmakers in Greece’s 300-seat parliament.

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