Contributed by: R. Ezra Mizrahi
Why would Hashem give the goyim a prophet, like Bilam, to help them in their conquests? Why would Hashem rest his divine presence on such an evil man?
Indeed this question is answered by Rashi. Our dear commentator tells us that the power of prophecy was given to Bilam to ensure that the gentile nations would not have this valid argument: that if Hashem would have given them a Navi, they would have been righteous and holy. Instead, Hashem did provide with Navi'im, but still the gentile nations breached their warnings in their evil actions.
But the problem still remains- can the gentile nations still complain: "Why did Bnei Yisrael received a Navi like Moshe and we did not? Had he received a Navi of Moshe's caliber, we would be different- instead you only sent us Bilam."
The nations of the world did not believe in Moshe Rabeynou for a simple reason: they did not believe in miracles outside of nature, created with the power of Hashem. Therefore, Hashem sent them a Navi, that could also perform miracles above nature, forcing them to accept that powers do exist above nature. Once they followed such a Navi, they could no longer doubt the validity of Moshe, the true Navi.
In addition, it is important to note that a leader's strength, power, and level of spirituality is defined by those people he leads. While the other nations level of spirituality earned them Bilam Ben Be'or, the spirituality of Bnei Yisrael earned them Moshe.