Final answer:
White Southern Democrats were the group that blocked the passage of federal anti-lynching laws throughout the 1920s, due to their desire to maintain regional control over social issues and resist federal civil rights mandates.
Step-by-step explanation:
The passage of federal anti-lynching laws in the 1920s was blocked by a specific political group. While several factors and entities played roles in the tumultuous racial dynamics of the time, the primary opposition to anti-lynching legislation came from white Southern Democrats.
Their united resistance was due to a variety of reasons, including the preservation of regional control over social issues and a refusal to acknowledge federally mandated civil rights. Over two hundred bills were introduced to make lynching a federal crime, but despite passing the House of Representatives on three occasions, none became law. This failure can be largely attributed to the systematic opposition from Southern Democrats who were committed to maintaining the status quo of racial hierarchy in the South. They resisted federal intrusion in what they deemed were state matters, even when it came to issues as severe as lynching.