"There has never been a good war, nor a bad peace"

I believe that war should be avoided at all cost. In many cases, a war can be easily avoided, especially in situations where one country invades another unexpectedly. However, if the only option available to prevent harm to multiple other countries is to wage war, then it would be acceptable. However, waging war in such an instance would probably result in further destruction, as the country which was initially suspected of hostility towards other countries would have a concrete reason to strike against them, under the pretense that "those countries' allies attacked us first". War is incredibly problematic, though, and not doing anything about the offending country could result in them successfully attacking other countries, thereby making it too late to save anyone else. My views about war are probably best summed up by a quote from T.H. White:

"There was such a man when I was young--an Austrian who invented a new way of life and convinced himself that he was the chap to make it work. He tried to impose his reformation by the sword, and plunged the civilized world into misery and chaos. But the thing which this fellow had overlooked, my friend, was that he had a predecessor in the reformation business, called Jesus Christ. Perhaps we may assume that Jesus knew as much as the Austrian did about saving people. But the odd thing is that Jesus did not turn the disciples into storm troopers, burn down the Temple at Jerusalem, and fix the blame on Pontius Pilate. "

War, in many cases, can be prevented through discussion and compromise. It does not have to be a bloody affair, simply one wherein both sides are able to understand each other.