Facing the threat of instant annihilation from atomic bombings, another world war is simply not an option for any reason or for any nation at any time, and the only option for mankind is the rational and peaceful resolution of its challenges, said a U.S. historian on Monday.

The atomic bombings of Hiroshima and Nagasaki in August 1945 in Japan opened a new chapter in the world history, said Paul A. Tenkotte, a professor of history at Northern Kentucky University.

"It is important to remember that the United Nations has managed to keep the world from a major global conflict for 75 years," Tenkotte told Xinhua in an email.

International negotiations are never easy, but certainly easier and less costly than any war, he said.

Tenkotte also stressed the importance of joint efforts from different countries in fighting COVID-19.

"It will require a concerted effort of every nation to defeat COVID-19, and to assure that 7.8 billion people worldwide receive vaccines when they become available," he said.

"That alone will require a massive international logistical effort," he added.