More than 40 percent of non-Hispanic African American men and women have high blood pressure, and roughly 42 percent of Black men age 20 and older have it as well.

In 1998, Dr. Grim the director of the hypertension research center at the Charles R. Drew University of Medicine and Science in LA, proposed that high rates of hypertension among African Americans could have arisen from the Middle Passage of slaves that lasted about 200 years.

The hypothesis states that Blacks who made it through the middle passage were those able to retain salt. I believe there are other factors like adequate medical facilities / medical care as well as environment factors and stress but this could be the largest factor.

https://www.encyclopedia.com/social-sciences/applied-and-social-sciences-magazines/slavery-hypertension-hypothesisc