What was first broken in 1954?

In 1954, the "color barrier" in professional sports was notably broken when the Brooklyn Dodgers signed Jackie Robinson, who became the first African American to play in Major League Baseball in the modern era. His debut in 1947 challenged racial segregation in sports and society, paving the way for future integration. Additionally, the United States conducted its first successful test of a thermonuclear device, known as the "hydrogen bomb," marking a significant advancement in nuclear weapons technology.