It is not constructive. (Affirmative sentence)

War is a curse for the human civilization. (Negative sentence.) = War is not a blessing/boon for the human civilization. 

It destroys civilization. (Interrogative sentence) = Doesn't it destroy civilization? 

It is the worst evil in civilization. (Positive) = No other evil in civilization is as bad as it. 

Those who are war mongers make the trouble for all. (Simple sentence) = War mongers make the trouble for all. 

We know that war brings destructions. (Passive voice) = It is known to us that destructions are brought by war. 

Shouldn't a man learn to live in peace? (Assertive sentence) = A man should learn to live in peace.