Why was the presence of slave markets in washington, d. c. so controversial

First because Washington, D.C. was the capital city, and second because the slave trade was not seen as a good thing by the eyes of the foreign.

Explanation:

England was the first country in the world to free its slaves (in 1826), and then it began to compelled other countries to follow the example. But the United States did not make this until the 1860s, and slave trade was common in American cities. In Washington, D.C., however, as the capital city, it was something bigger. It was the center of the abolitionist campaign, but this was in contrast with the slave trade and slave markets.

the constitution of the united states gave congress the absolute authority over immigration laws

presidency should be the title