Historically the first philosopher to enquire deeply into the nature of corruption in society was Ibn Khaldun (1322-1406), whose wandering life was largely spent in the northern littoral of Africa at a time when kingdoms and sultanates were crumbling.
Conquest, tyranny, treachery, and the clash of cultures bring about corrupt societies, and so does old age. Sometimes the five faces of corruption are visible at the same time.
Corrupt men are always liars. Lies are their instruments, their pleasure, their solace. In time they come to believe their lies, or rather to half-believe them.