As we are into the season of goodwill to all men (and women and others) and peace on earth it seems churlish to complain that the Leader of The Labour Party lends support to a body named "Stop The War". He has been prominent in it for some time so why complain now?
Guido Fawkes gives a list of matters where this body is alleged to have misjudged situations. What this list also tells us is the problem of deciding what war is going on, why, involving whom and to what purpose. History tells us that a good deal of it is not new just repeating what has happened so often in the past.
Having consulted my dentist only yesterday, I can confirm that I am long and tender in the tooth. But there has been war in the world ever since my first one appeared and had been before for at least a few millennia. It is likely that on every day in my life armed conflict was happening somewhere for some reason.
In principle, the prevention and avoidance of war ought to be one of the highest aims of our leaders. These days they do spend a lot of time talking to each other and we have not had major powers in direct conflict quite so much as in the past. They realise the costs and the danger, not least of losing power.
But at the same time many powers now often involve themselves in the many small wars and related disputes as an alternative. Also, it provides a major source of profit for major powers with large arms industries. These can be called "proxy wars".
One reason that this option is available is because in the world there are many groups that dislike and indeed hate each other for a variety of ancient reasons and some of these and others have land and water rights and boundary issues that they cannot resolve peacefully, or often do not want to.
Essentially, all you need is a mad or highly ambitious leader with cronies who see local or internal wars as necessary to their function or survival. If they have enough spare loose young men to hand and they can be persuaded, a very easy thing to do, then you will have such wars. Add a spice of political or other fundamentalism to it and you can keep it going for as long as possible.
In the late 19th Century and early 20th Centuries, the great powers of Europe divided up the world into "Empires" to try to avoid wars between themselves. They did not succeed, but they did at least contain the waging of small wars within their fiefs. It did not do them much good as the local populations were ungrateful.
You can only really stop these wars if the relevant sides have become exhausted or wholly ruined. You might have a chance if their leaders can accept that all have too much to lose, but with mad or ambitious men this is far from easy. One way much favoured in history is for someone to eliminate the other, see the picture above of The Last Stand Of The 44th At Gandamak.
Looking at the Middle East at present we have major powers with a "hit or miss" approach, minor powers adding to the confusion and internal groups with mutual hatreds that cannot be ended, only perhaps accepting an uncertain truce.
Worse is that some elements are now trying to export the conflicts of the Middle East to the home territories of major powers, albeit on a small scale. But you do not need large scale activity, for example, to wreck a tourist industry or a property dependent economy such as that of the UK.
The Stop The War people are unlikely to succeed because what is going on over there could be one of those never ending wars like so many in past history. It has all the hallmarks of this. At the same time indulging in a low level proxy war with bombs is not going to stop small scale attack units arriving in Europe.
So finding the answer to the question in the title looks to be beyond the abilities of any of our political parties given their current other policies. The radical change in thinking, policy and actions needed are alien to any of their ideas or structures.