what are these paragraphs mean (just clarify for me ,i got the whole meaning)
It is an unquestioned principle that has dominated international thinking for decades:we live in an overcrowded world teeming with billions of humans (who are destined to suffocate our cities and squeeze our planet of its precious resources .our species is inexorably wrecking Earth)(describe this part) (our future is destined to be nasty brutish,and cramped) .Population analysts have suddenly started to question the "self-evident"truth that we are destined eventually to drown under our own weight)(I know the whole meaning but what is the meaning of started to question...till end) .while accepting that populations will continue to rise,(they point out that this rise will not be nearly steep or as long-lasting as once feared)(meaning this)(there will be no workforce if people do not have children) (meaning).(in china, the state enforces quotas of offspring number,and it is expected that its population will peak at 1.5 billion)

Question

what are these paragraphs mean (just clarify for me ,i got the whole meaning)
It is an unquestioned principle that has dominated international thinking for decades:we live in an overcrowded world teeming with billions of humans (who are destined to suffocate our cities and squeeze our planet of its precious resources .our species is inexorably wrecking Earth)(describe this part)                 (our future is destined to be nasty brutish,and cramped)                .Population analysts have suddenly started to question the "self-evident"truth that we are destined eventually to drown under our own weight)(I know the whole meaning but what is the meaning of started to question...till end)                            .while accepting that populations will continue to rise,(they point out that this rise will not be nearly steep or as long-lasting as once feared)(meaning this)(there will be no workforce if people do not have children) (meaning).(in china, the state enforces quotas of offspring number,and it is expected that its population will peak at 1.5 billion)

Answer

"who are destined to suffocate our cities and squeeze our planet of its precious resources .our species is inexorably wrecking Earth"
This means that the billions of humans are going to overcrowd cities, and deplete the planet's resources (e.g. oil, fossil fuel). The human race is destroying Earth in a way that cannot be stopped or changed.

"Population analysts have suddenly started to question the "self-evident" truth that we are destined eventually to drown under our own weight"
This means that population analysts have suddenly began doubting whether it is really true that we will someday destroy ourselves due to our own actions.

"they point out that this rise will not be nearly as steep or as long-lasting as once feared"
This means that the increase in population will not be as much, and will not last as long as we had worried about in the past.

"there will be no workforce if people do not have children"
This means there will not be enough people to do work if people do not give birth to children.

Hope my rephrasing helps!