Ignorance.

The primary, the most urgent requirement is the promotion of education. It is inconceivable that any nation should achieve prosperity and success unless this paramount, this fundamental concern is carried forward. The principal reason for the decline and fall of peoples is ignorance.
The publication of high thoughts is the dynamic power in the arteries of life; it is the very soul of the world. Thoughts are boundless sea, and the effects and varying conditions of existence are as the separate forms and individual limits of the waves; not until the sea boils up will the waves rise and scatter their pearls of knowledge on the shore of life….

‘Abdu’l-Bahá, The Secret of Divine Civilization