How do you know that they failed if you never looked at the prophecies and what happened later that fulfilled them?
A failed prophecy is a prophecy that 'fails' to predict an event that happened later. Baha'u'llah did not fail to predict the atomic age so His prophecy did not fail. It is that simple.
From the book:
The Challenge of Baha'u'llah, pp. 85-86
The coming dawn of the Atomic Age was writ large in the prophecies of Baha'u'llah and 'Abdu'1-Baha.
Nuclear Terror
Prophecy 21: The development of nuclear weapons.
In a Tablet entitled
Words of Paradise (written shortly before His passing in 1892), Baha'u'llah noted the rush by Western civilization to develop ever-more-deadly weapons of war. Explaining the urgency of His call for world unity and peace, He declared:
Strange and astonishing things exist in the earth but they are hidden from the minds and the understanding of men. These things are capable of changing the whole atmosphere of the earth and their contamination would prove lethal.141
This reference to 'strange and astonishing things' aptly describes the twin processes of fission and fusion by which we obtain nuclear energy. The reality of such a power was again affirmed in 1911 by 'Abdu'1-Baha:
There is in existence a stupendous force, as yet, happily, undiscovered by man. Let us supplicate God, the Beloved, that this force be not discovered by science until spiritual civilization shall dominate the human mind. In the hands of men of lower material nature, this power would be able to destroy the whole earth.142
'Abdu'1-Baha spoke these portentous words to the Japanese ambassador to Spain, Viscount Arawaka, for whose country the warning carried grave implications.
An ironic coincidence? If so, it was not the only one. In 1920 'Abdu'1-Baha wrote to a group of young students in Tokyo: 'In Japan the divine proclamation will be heard as a formidable explosion .. .'U3 (I am aware of no other explosion metaphor in the Baha'i writings.) A quarter of a century later, the Japanese cities of Hiroshima and Nagasaki were vaporized in the first wartime use of atomic bombs. Today the world's nuclear arsenals contain enough firepower not only to destroy humanity many times over but to alter climate and atmosphere so drastically as to render the planet uninhabitable.