According to historical perspective, the reason Persia was ultimately unsuccessful in conquering Greece at the Battle of Marathon is that "Persia had fewer soldiers than Greece to fight its battles."
This is because, during the Battle of Marathon, Persia only had less than 30,000 soldiers.
Another reason was that the Persian cavalry was not involved in the battle.
The Battle of Marathon was fought on the 12th of September, 490BC.
Hence, in this case, it is concluded that the correct answer is option A. "Persia had fewer soldiers than Greece to fight its battles."
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