The high voltage direct current (HVDC) system connected with weak AC system is considered to be one of the causes for voltage instability.

与弱交流系统相连的高压直流系统被认为是引起电压不稳定的一个因素，评价交直流系统电压稳定性的方法相当复杂。

youdao

Throughout the world, one of the most prevalent causes of war, terrorism, and political instability is the ongoing weakening of the nation-state system.

CENTERFORSECURITYPOLICY: Islam and the nation-state