I saw a documentary about what would happen to modern society globally if there were a large solar eruption. It happens all the time but a really powerful magnetic storm could lay waste to human infrastructure. And in fact, there is a historical precedent....
"The solar storm that knocked out telegraph service was known as the "Carrington Event," which occurred in 1859, where a powerful geomagnetic storm caused disruptions to telegraph systems around the world, with operators experiencing sparks and even fires due to the induced electrical currents in the wires. "
That was when the only electronics in the world was telegraphs. Imagine the havoc something like that would cause today with all of our power grids, networks and satellites.