The demographics of black people have always been off. There is no way the government when they initially started the census would want to have a true accurate number of black people in America since they were never considered as people at the beginning of the country. For one a Census is a good way to also maintain control and disenfranchise people. The black population was probably around 30-33% after the Civil War. Blacks were a majority in almost all southern states which is why they dominated southern politics with carpetbaggers from the North during Reconstruction. Then there was mass immigration from Europe in the 1900s to dilute the black population. The whites were expected the participate in the industrial revolution, which was the main beef that the North had with the South. The North didn't fight against slavery, they were fighting for an industrial revolution because the rest of the world was leaving America behind.
By the time it was 1900, the black population was around 9-10% according the government. Now peep, that white immigration from Europe into the 1930s with zero immigration from for blacks to enter in, making black people a perpetual minority, Then, fast forward to the so-called white baby boom after WWII, blacks still hovering around 9-10%. How is that possible with zero immigration? Well, cacs knew that black people are very good at having babies. For this reason, Planned Parenthood and the Eugenics did a lot of shyt to curb the birth rates among black people. Go to the late 1960s, when immigration reform allowed for non-whites outside of blacks to pour into the country. Why? Blacks were experiencing new social freedoms and whites needed to create buffer groups to slow black progress. This is when the US started seeing an higher increase of Asians, Middle Easterners, and the so-called Latino which came out of nowhere. "Latinos" before the immigration reform were either classified as white or colored depending on the part of the county they were in and if they could pass as white. Think Sofia Vegera passing as white and Zoe Saldana being colored. Mexicans (chicanos) in Texas were going to school with white people, including all the major universities while blacks were held out. In fact, Mexicans in Texas back in the day were white on the Census. Now fast forward again, black people by 1990 are about 12% of the population according to the government, with little outside immigration until the 1970s which was still minor compared to other groups. If Mexicans were not crossing the border every second from 1970 til now. The black population would be closer to 18-21% easy. Meaning that the white population is still having trouble growing. Because the less people immigrating into the country, means we are increasing because whites have a hard time having children, notice that the Europe is seeing decreases in population.