Rush Limbaugh claimed that white people had done more to end slavery than any other race. It is unclear where he got this idea from.
In the 17th and 18th centuries, white people forced African people into slavery, primarily in the American colonies. These enslaved people were exploited to work on tobacco fields and cotton crops.
The U.S. Emancipation Proclamation was issued in 1862 by U.S. President Abraham Lincoln. It declared that "all persons held as slaves, shall be then, thenceforward, and forever free."
The 13th amendment formally abolished slavery in the U.S. in 1864. However, it did not apply to large parts of the U.S., and just because Abraham Lincoln was white doesn't mean that white people were responsible for the end of slavery, especially when white people instigated the transatlantic slave trade in the first place.
As the Independent reports, "at least 10.7 million black Africans were transported between the two continents. A further 1.8 million died en route." The U.N. has said that the transatlantic slave trade was "one of the greatest atrocities in history," adding that the "unparalleled global tragedy claimed untold millions of lives over four centuries, and left a terrible legacy that continues to dehumanize and oppress people around the world to this day."
In his lifetime, Rush Limbaugh expressed a wide variety of racist views. In 2014, he said that the Obama administration lacked the requisite enthusiasm to fight the Ebola virus because of slavery, claimed that Obama disagreed with Limbaugh's interpretation of the Constitution as it permitted slavery, and argued that 12 Years a Slave won the Academy Award for Best Picture because it was about slavery.