You are about the first person to agree with me on this! Most people, especially with reference to WW2, talk about moral imperatives, but to me the biggest moral imperative for any government is to look after its own people. That, to me, means not taking them into avoidable wars.
As to whether there would have been a Geat War without Britain, it's hard to say. Certainly the absence of British troops would have shortened the stalemate in France, and problaby led to a peace treaty by about 1916, if not earlier, in which France would have had to cede much of its Eastern territory (Alsace/Lorraine) and accept German hegemony in Western Europe. Germany would have scooped up most if not all of Frances' overseas colonies as well. Not that that would have brought them to anything like an equivalent of Britains' overseas possessions.
In the East, the Russian Revolution was inevitable, but if the Central Powers by then no longer had a Western Front to bother with, it is likely that a peace might have been reached earlier, and the final Bolshevik Revolution delayed or even avoided altogether. The Soviet Union, at least in the form we remember, might never have arisen.
If Britain had stayed out of the European conflict, it is probable that the US would also have done so. Given that the 'Spanish flu' pandemic of 1918 spread so rapidly in large part due to the concentration of men in military bases and camps, it is possible that this also might have been mitigated in both countries.
All that said, of course, there is still the matter ofthe Great Depression, an event which had few if any links with the Great War, but was a contributory factor to the rise of Nazism in Germany and thus WW2.
It's likely that the Depression would have caused disruption in all countries involved. In Germany, the continued semi-autocratic rule of the Kaiser would have come under pressure, resulting in either a Republic or a constitutional monarchy, France, on the other hand might well have gone either Left or Right. Left, and a Socialist or Communist regime would have been established, which might have been able to negotiate with the new government in Germany. Right, and we have a diferent scenario.
Imagine a nationalist, militarist France with, say, Charles de Gaulle as the dictator. There would have been attacks on both Britain and Germany. How would that play out, I wonder?
