TEMBISA, South Africa — When Morris Sello arrived in Johannesburg from his home province of Limpopo in 1994, his horizons seemed limitless. Apartheid, the oppressive hand that smothered opportunity for black people for decades, was gone. He dreamed of a slice of the life white South Africans had enjoyed for years: a good job, a house, a car, good schools for his children.

He found a job as a truck driver. But nothing else has worked out the way he planned. Instead of a house, he lives with his wife and four children in a fetid shack in this sprawling township. A car is unthinkable. The local schools are abysmal, and his faith that his children will do better in life is ebbing.

“I hope they can do better,” he said, a mix of resignation and despair in his voice. “I hope.”

Mr. Sello was among tens of thousands of workers to walk off the job in the biggest wave of labor unrest to hit South Africa since the end of apartheid. Wildcat strikes by gold, platinum and iron ore miners have crippled one of South Africa’s most important industries, prompting the nation’s first credit rating downgrade in nearly two decades and a slide in the country’s currency, the rand, to a three-year low.

And the troubles are far from over. The truck drivers have ended their nearly three-week strike, but not before causing food and fuel shortages that sent shudders through an already struggling economy. The mine strikes have dragged on, and some municipal workers have announced plans to join the picket lines as well.