The batch of more than 3,000 Russian-bought ads that Facebook is preparing to turn over to Congress shows a deep understanding of social divides in American society, with some ads promoting African-American rights groups including Black Lives Matter and others suggesting that these same groups pose a rising political threat, say people familiar with the covert influence campaign.

The Russian campaign — taking advantage of Facebook’s ability to simultaneously send contrary messages to different groups of users based on their political and demographic characteristics — also sought to sow discord among religious groups. Other ads highlighted support for Democrat Hillary Clinton among Muslim women.