Which of the following categories was the first to be protected by federal law against discrimination in housing?

The category of race was the first to be protected by federal law against discrimination in housing. This foundational protection was established by the Fair Housing Act of 1968, which was part of a broader effort to eliminate discrimination and promote equal housing opportunities. The Act primarily aimed to address the racial segregation that was prevalent in many areas at that time, reflecting the civil rights movement's focus on combating racial injustice.

By including race as the first category for protection, the legislation recognized the urgent need to address the disparities faced by racial minorities in housing access. Subsequent amendments and laws have gradually expanded protections to include other categories like sex, familial status, and sexual orientation, but race remains the initial focus that catalyzed broader discussions about discrimination in housing.