There are many references to the assassination of President John F Kennedy. Among them, the victim in this episode is Mayor Alec Hidell. Alek Hidell was an alias used by Lee Harvey Oswald, the assassin of JFK. Also, the plot of this episode (a marksman using a sniper from a window to assassinate a political figure in an open-top vehicle) is a reference to the Kennedy assassination.
The event celebrated by the Protestants on Orange Day was the Battle of the Boyne in 1690 between the Catholic James II and the Protestant William III of England (a.k.a. William of Orange / William II of Scotland), who, with his wife, Mary II (his cousin and James' daughter), had overthrown James in England in 1688. The battle took place in Oldbridge, County Meath on Ireland's east coast, resulting in a Protestant victory and Protestant control of Ireland.
This episode takes place in 1899.