My teacher once asked the class about a certain topic: Do we learn from war? (I believe he started talking about it and mentioned about a really smart Indian man who some thought was the true Messiah. I can't remember his name :'( )
This is my own answer:

Ultimately, NO.
Although we do learn how to make bigger, badder, and more dangerous weapons, that is for the sake of creating more battles, conflicts, and war.
If we learned from war, there probably wouldn't be any more wars. Do you get what I mean?
If we did learn that war is bad and dangerous and...unhelpful, there would be world peace.
Apparently, there are some people out there who want more power, land, and control, etc. -.-

Which leads to my next topic: How should one decide when a cause is worth fighting for? (Got this idea as an assigned essay topic)
They don't decide. ALL causes are (automatically) worth fighting for, because it is only human to fight for things that are important to a person or people.
Sure, some of those causes could be meaningless/stupid/worthless/unhelpful-to-the-world, but it is still a cause that a person believes in.

Weellll then.
Now I need to finish my essay about the second topic I just wrote about . ____ .

Ta ta for now! (what does that even mean? I've heard of it somewhere, but I can't remember where. Pooh bear??? )