underdeveloped
adjective uk/ˌʌn.də.dɪˈvel.əpt/ us/ˌʌn.də.dɚˈvel.əpt/
C2 （尤指国家）不发达的
(especially of a country) without modern industry or modern services that provide transport, hospitals, etc.
an underdeveloped country 欠发达国家
It's in the poorer, underdeveloped eastern region of the country that the biggest problems exist. 最大的问题存在于这个国家较为贫穷落后的东部地区。