BUENOS AIRES, Argentina—As lights turned back on across Argentina, Uruguay and Paraguay after a massive blackout that hit tens of millions people, authorities were still largely in the dark about what caused the collapse of the interconnected grid and were tallying the damage from the unforeseen disaster.
Argentine President Mauricio Macri promised a thorough investigation into what he called an “unprecedented” outage, one that raised questions about flaws in South America’s grid, which connects many of the region’s largest countries.
