The major three things or lessons learnt from the World W.a.r. 1 are the following: W.a.r. is always unpredictable, History should be remembered, and Exhaust diplomacy before you use force. Read below about diplomacy.
What is diplomacy?
Diplomacy is the main instrument of foreign policy which represents the broader goals and strategies that guide a State's interactions with the rest of the world.
Therefore, the correct answer is as given above
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