Finally, the population is growing rapidly, but the job opportunities are limited, which leads to such a situation that people who used to live well are put in a very poor position.
What don't you understand?
The last adverb
Population is the theme.
Is increasing is a predicate verb.
High speed is an adverbial.
But a conjunction, indicating a turning point.
Job opportunities are the theme.
Is is a predicate verb.
Limited is a predicative.
This is a conjunction indicating causality.
What leads to a situation is that the present participle is used as the adverbial of result.
Those who once lived a rich life were put in a terrible situation. This is an appositive clause of a situation.
Where "through" is the subject who once lived well "is the attributive clause of" through "
It is the predicate verb of a clause.
A terrible condition is the object.