500
Why (and how) did the deaths of millions of poor workers lead to a major change in the ability of poor people to have some control and influence over their own lives?
Fewer workers meant that each worker had more value. Lords had to treat their workers better, or those workers might find somewhere else to go. Since there was a lot of work to be done (and fewer people to do it), workers were able to pick and choose jobs based on their own needs. This led to workers having more power, control, and value.