What Failure of Pre-Revolutionary Governments Often Leads to Their Overthrow

What failure of pre-revolutionary governments often leads to their overthrow by revolutionary forces?

A) It has sharply increased taxes
B) The country has been defeated or greatly weakened in a war
C) High-ranking government officials defect to the revolutionary movement
D) The government alienates powerful countries in the region
E) The country has suffered natural disasters such as a drought or flooding