The answer is C. World War 2
The Admission to the Union Clause of the United States Constitution, oftentimes called the New States Clause, and found at Article IV, Section 3, Clause 1, authorizes the Congress to admit new states into the United States beyond the thirteen already in existence at the time the Constitution went into effect.
They used interchangeable parts. This made the mass production possible and caused it to happen.
They were displaced by white American settlers again.