The answer is that we do not expect the nations of the world to accept the Torah as authentic, for they never stood at Sinai, nor do they have the benefit of an unbroken chain of Torah transmission. We, however, must know that our right to Eretz Yisrael comes from the Owner of the World, and our title-deed to Eretz Yisrael is His Torah. All the animals of creation view the world through their senses. They know only what they see, smell, hear, touch and taste. Their world is bounded by immediate perception.
Man is different.
The very essence of man, for that is his name, his defining quality, is his imagination. Only Man can take what he perceives and compare, analyze and extrapolate. This is the comparison between man and his Creator. With one exception. The creation of Man.