One hot Saturday in August 2014, Sandra Tamari scrolled through social media and learned that a Black teenager named Michael Brown had been fatally shot by a police officer in nearby Ferguson, Mo. Her heart “just sank,” she recalled, when she learned that Mr. Brown’s mother had stood on the other side of the police tape while her son’s body had been lying in the street for hours.

Ms. Tamari, who is Palestinian American and lives just outside St. Louis, had spent the previous weeks mourning the death of Muhammad Abu Khdeir, a 16-year-old Palestinian boy. He had been kidnapped, bludgeoned and burned to death in Jerusalem by Israeli teenagers avenging the killings of three Israeli teens by Palestinians. The incident was part of a cycle of violence that culminated in the 2014 War in Gaza that summer, which killed more than 70 Israelis and more than 2,200 Palestinians.

“I was already in so much grief about what was happening in Palestine,” she said. She could not shake the parallels in her mind between Michael and Muhammad. To her, they were both teenagers stolen from their families by racially motivated violence.

A week later, she and about 15 members of the St. Louis Palestine Solidarity Committee joined the protests that sprang up after Mr. Brown’s killing. Before they left, her husband grabbed some old white cloth and made a banner that read: “Palestine Stands with Ferguson.”

A decade later, the Palestinian cause in the United States has become tightly intertwined with the much more powerful African American quest for civil rights — an alliance that has been both strengthened and tested in the four months of war since Hamas killed more than 1,200 people in Israel.

African American writers, leaders, athletes and celebrities have spoken in support of Palestinians as Israel’s bombardment of Gaza pushes the number of dead past 26,000 people.