There is a nice discussion this here: Merriam-Webster's Learner's Dictionary
See specifically this:
Subjected to means "to cause or force (someone or something) to experience (something harmful, unpleasant, etc.)."
"Race car engines are subjected to extreme performance demands." ["Race car engines are forced to experience extreme performance demands."]
By contrast, subject to means "affected by or possibly affected by (something)" or "likely to do, have, or suffer from (something)" -- more neutral ideas that indicate a state of being or a fact:
"This area is subject to flooding." ["This area is likely to have flooding."]
People do die - it's a fact. To say they are "subject to" death could makes it sounds like some don't actually die, but it's still technically okay.
However, unless you're writing about people who were killed by others (i.e., they were forced to experience it), then "subjected to" is not right.
Student or Learner