Question:  Leonard "Len" Benker Johnson organized a concert and a rally featuring an American bass singer who became involved with what?

Context paragraphs:
Pearce Johnson: Pearce B. Johnson was a part-time sports editor for the "Providence Journal" and the general manager of the Providence Steam Roller of the National Football League.  He was also one of the original founders of the team and served as the team's manager throughout its entire history (1916-1933).  He is best known for hosting the very first night game in NFL history.  After the team ended play in 1931, Johnson organized a semi-pro version of the Steam Roller in 1932 to play small-scale local teams.  He also managed a minor league version of the Providence Steam Roller in the American Association in the 1940s.  Later in life, he became a football historian for the Pro Football Researchers Association and was at one time their oldest member.

Nick Massi: Nicholas E. Macioci (September 19, 1927 – December 24, 2000), known as Nick Massi, was an American bass singer and bass guitarist for The Four Seasons.

Gene McDonald: Gene McDonald is an American bass singer and was the bass vocalist for the Florida Boys southern gospel quartet from 1998-2007.

William F. Hooley: William F. Hooley (16 April 1861 – 12 October 1918) was a British-born American bass singer and pioneer recording artist who was popular as a solo singer, as a monologist, and as a member of several of the most successful vocal groups of the early twentieth century, including The Haydn Quartet and The American Quartet.

Richard Sterban: Richard Anthony Sterban (born April 24, 1943) is an American bass singer born in Camden, New Jersey, who joined the country and gospel quartet The Oak Ridge Boys in 1972.  Prior to joining The Oak Ridge Boys, Sterban toured with J. D. Sumner and the Stamps Quartet, who were singing backup for Elvis Presley at that time.  Sterban ultimately became best known for his "oom-pa-pa-oom-pa-pa-mow-mow" bass solo in the Oak Ridge Boys' 1981 single "Elvira" and sang lead vocals on a select few of the group's songs, including a cover of The Righteous Brothers' hit "Dream On," which itself became a hit.

Len Johnson (boxer): Leonard "Len" Benker Johnson (22 October 1902 – 28 September 1974 (aged 71)) born in Clayton, Manchester was an English professional middle/light heavyweight boxer of the 1920s, and 1930s, who won the Australian version of the British Empire middleweight title in 1926.  Johnson (who was of mixed race) was denied the opportunity to fight for championships in Great Britain because of the colour bar that existed in boxing at that time.  He was managed by his father Bill Johnson.  Johnson fought on boxing booths in the 1920s, and from 1930 to 1939 owned his own travelling booth.  Just prior to the outbreak of World War Two Johnson briefly tried his hand at professional wrestling, but once war came he lost interest in both boxing and wrestling, and sold his booth.  During World War Two Johnson was a member of the Civil Defence heavy Rescue Squad in Manchester.  Len Johnson was also a member of the Communist Party of Great Britain (joining the party in 1944 and later writing a boxing column for the party newspaper "The Daily Worker"), a trade unionist, a community leader in Moss Side, a local civil rights activist, and attended the 5th Pan-African Congress in Manchester.  Following the Second World War, he was a co-founder of the New International Society in Manchester, which provided a vehicle for black political and social self-organisation in the city and campaigning against racism at home and abroad, including organising a concert and a rally featuring Paul Robeson in support of the Trenton Six, which were both attended by 10,000 people.

George Younce: George Wilson Younce (February 22, 1930 – April 11, 2005) was an American bass singer, known for performing with Southern gospel quartets, especially The Cathedrals.

Paul Robeson: Paul Leroy Robeson (pronounced ; April 9, 1898 – January 23, 1976) was an American bass singer and actor who became involved with the Civil Rights Movement.  At Rutgers College, he was an outstanding American football player, and then had an international career in singing, with a distinctive, powerful, deep bass voice, as well as acting in theater and movies.  He became politically involved in response to the Spanish Civil War, fascism, and social injustices.  His advocacy of anti-imperialism, affiliation with communism, and criticism of the United States government caused him to be blacklisted during the McCarthy era.

Larry Gene Ashbrook: Larry Gene Ashbrook (July 10, 1952 – September 15, 1999) was an American mass murderer who killed seven people and injured a further seven at a post See You at the Pole Rally featuring a concert by a Christian rock group Forty Days before committing suicide.  It occurred at Wedgwood Baptist Church in Fort Worth, Texas, on September 15, 1999.

Ryan Allen: Ryan Allen is an American bass singer best known for his work in opera.  He has performed professionally in all 50 states, appeared with numerous American opera companies, and sung as a soloist in Russia, Israel, Poland, Norway and Sweden.

Supporting paragraphs: Len Johnson (boxer) Paul Robeson
Answer: the Civil Rights Movement