Additional social stresses may also occur because of the population explosion or problems arising from mass migration movements—themselves made relatively easy nowadays by modern means of transport.
句子主干结构是Additional social stresses may also occur；because of后面有两个宾语the population explosion 和 problems；名词problems带有现在分词短语作后置定语arising from mass migration movements； themselves作为代词，指前面的名词短语mass migration movements，充当同位语作用，后面的过去分词短语made relatively easy是themselves的后置定语，by modern means of transport是方式状语，解释变得容易的原因。
population explosion 人口爆炸
arise from 源自于
means of… 的方式
A lateral move that hurt my pride and blocked my professional progress prompted me to abandon my relatively high profile career although, in the manner of a disgraced government minister, I covered my exit by claiming “I wanted to spend more time with my family”.