- May 7 Argentina & Brazil sign a navigation pact
- May 15 2nd San Francisco Vigilance Committee organized
- May 19 Senator Charles Sumner of Massachesetts speaks out against slavery
- May 21 Lawrence, Kansas, is captured and sacked by pro-slavery forces
- May 22 Violence in the US Senate, South Carolina rep Brooks uses a cane on Massachusetts Senator Charles Sumner
Event of Interest
May 24 Pottawatomie Massacre: John Brown and abolitionist settlers kill five pro-slavery settlers in Franklin County, Kansas
John Brown
- May 27 Doctor William Palmer (the Rugeley Poisoner ) found guilty of poisoning in Stafford, England