On the contrary if a day of battle is claimed to have occurred we can go look for its remnants on the field, corroborate with independent sources, infer from indirect impact on other events etc. Even then we generally have valuing degrees of confidence that either the event happened or it happened as described. Also these events all obey known science, no claims of Caesar raining the thunderbolts of Zeus on his enemies for example.
That limits to a very specific kind of history. More parts of history is about what some historical figures did and said which can hardly be evidenced.
Christianity on the other hand does not even achieve much if any of this level of evidence yet then expects is to believe that events defied physics and we should base our lives around its lessons (no matter how stupid some sound). Do you see why your comparison with "normal" history is flawed?
Apples and oranges, not every scenarios share what is common to known wars. Most of them can only be conveyed by witnessing. Answer me, how can a sentence said by a historical figure be evidenced?
The trick is, no witnessing can be made more valid then those martyred themselves for what is said and done.