Surge by Populists Leaves Italy Without Clear Victor

ROME—Italy’s national elections yielded no outright winner, initial projections showed, likely ushering in a protracted period of political instability and tension in the eurozone’s third-largest economy.

Populist parties staged a strong showing on Sunday, winning about half of all votes cast, according to the polls, underscoring the depth of anger among Italians at the country’s direction and the continued power of right-leaning populist parties in European politics.