In short, almost all military victory or defeat can be explained not by numbers or equipment, but simply by which side had more experience and practice.
Stephen Biddle sums it up very well in Explaining Victory and Defeat - in a short modern war, the side with the greater readiness will win 100% of the time, regardless of the other variables. In a long war, the incompetent army can "learn the hard way" until they negate this advantage.
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