He was unable to prove his theory because he didn't have any proof.
The answer might be sugar beets. But I'm not positive.
The correct answer for the question that is being presented above is this one: " Mexican-american war and the California joining the union as a state." The two events that fueled the debate over slavery between 1846-1850 are the Mexican-american war and the <span>California joining the union as a state.</span>
B. <u>"a collection of tribes who began crossing the Hindu Kush into India in 1500 BCE"</u>