Ferguson argues that in the war crisis of 1914, the Liberal cabinet was split. So far, so good. It is only when all the variables and factors are arrayed can we say that, yes, keeping the Tories out was the decisive issue. But Ferguson does not do that. And that is because he cannot do it.
History is too messy for real predictions to emerge from conflicting and incomplete evidence.
Other examples abound. On page 169, he argues that German war aims without British entry into the war would have been less grandiose than they rapidly became. It is as if Britain precipitated Germany's territorial claims in September 1914. This is almost certainly mistaken, and flies in the face of evidence about high rates of voluntary enlistment later in 1914, when the disruption of trade occasioned by entry into war was damped down. Once again, this is an historical statement about plausible outcomes based on insufficient data.