Check, please!!!

[Slam Juice]

Уверенность его базируется не на обладании некой закрытой информацией, а лишь на собственном умении оценивать обстоятельства, которые могли бы привести к войне.

Powell’s assurance is based not on having some confidential information but on his own ( personal ?) ability to estimate the situation that could lead to a war.

[triplet]

Вариант:
His confidence comes from his own ability to evaluate circumstances/events that may lead up to war rather than him being privy to some closely held information

[langkawi2006]

а если не "closely held", а "qualified"?

[onlys]

inside information ?

[donkey_hot]

restricted/classified info
imo

[Slam Juice]

Thanks a lot!

[Nina79]

His confidence is due to/comes from/is the result of/ his ability to effectively analyse situations and circumstances which could later become catalysts for war rather than from his being privy to confidential information.