Thousands of protesters took to the streets of Bangladesh on Monday to protest after a massive fire at a garment factory in Dhaka trapped and killed at least 120 workers on Saturday. The factory fire, Bangladesh's worst ever, was followed just two days later by another blaze in a different factory, injuring 10 people. Bangladesh's garment industry is among the world's biggest exporters of clothing — second only to China — and according to ABC News, many of the workers who died in Saturday's fire were working overtime to make clothes for major American retailers like Walmart and Target. Here, what you should know: 

What do we know about these factories? 
The Tazreen Fashions factory, where Saturday's deadly blaze killed more than 100 people, opened in 2010 and employed roughly 1,500 workers who made T-shirts, polo shirts, and fleece jackets. The factory had sales of $35 million a year. It exported clothes to the U.S. and Europe and manufactured for a Hong Kong-based trading company called Li & Fung, which buys clothes for big retailers like Target and Walmart. 

What caused these fires?
We don't know for sure, though the local fire department reportedly suspects electrical problems or sparks from a cigarette. Both fires started in areas where large amounts of fabric and yarn were kept. The larger of the two blazes started on the ground floor of the Tazreen factory and spread quickly, trapping workers on the higher floors of the nine-story building.  

Why were so many people killed? 
A lack of fire escapes, mostly. There were no exterior fire escapes in the Tazreen factory, and many people died of smoke inhalation, while others died jumping from windows.

Are American industries at all responsible?  
Since 2006, more than 500 Bangladeshi workers have died in factory fires, reports The New York Times. Factories like these make clothes for brands like Tesco, Walmart, JC Penney, and H&M. While the fires certainly weren't directly caused by any of these brands, many human rights groups argue that American companies shouldn't do business with factories that employ workers in such dangerous conditions and for such little pay. "These brands have known for years that many of the factories they choose to work with are death traps," says Ineke Zeldenrust, the international coordinator for the Clean Clothes Campaign. "Their failure to take action amounts to criminal negligence." 

What do the U.S. companies say?
Many have been silent, according to ABC. But Walmart, for its part, issued a statement: "Our thoughts are with the families of the victims of this tragedy. ... [F]ire safety is a critically important area of Walmart's factory audit program and we have been working across the apparel industry to improve fire safety education and training in Bangladesh." Walmart actually flagged the Tazreen factory in May 2011 as being at "high risk" for unsafe conditions — and reportedly stopped working with many Bangledeshi factories over such risks — but has yet to confirm whether the Tazreen facility is still one of the U.S. mega-company's suppliers. 

Sources: The New York Times, Wall Street Journal, ABC News, CNN