Beheading was degraded to a secondary means of execution, including for treason, with the abolition of drawing and quartering in 1870 and finally abolished by the Statute Law (Repeals) Act 1973. One of the most notable executions by decapitation in Britain was that of King Charles I of England, who was beheaded outside the Banqueting House in Whitehall in 1649, after being captured by parliamentarians during the English Civil War. Celts
The Celts of western Europe long pursued a "cult of the severed head", as evidenced by both Classical literary descriptions and archaeological contexts. This cult played a central role in their temples and religious practices and earned them a reputation as head hunters among the Mediterranean peoples. Diodorus Siculus, in his 1st-century Historical Library (5.29.4) wrote the following about Celtic head-hunting:

They cut off the heads of enemies slain in battle and attach them to the necks of their horses. The blood-stained spoils they hand over to their attendants and striking up a paean and singing a song of victory; and they nail up these first fruits upon their houses, just as do those who lay low wild animals in certain kinds of hunting. They embalm in cedar oil the heads of the most distinguished enemies, and preserve them carefully in a chest, and display them with pride to strangers, saying that for this head one of their ancestors, or his father, or the man himself, refused the offer of a large sum of money.
Syrian rebels attempting to overthrow the Syrian government have been implicated in beheadings too. North America
Mexico
Miguel Hidalgo y Costilla, Ignacio Allende, José Mariano Jiménez and Juan Aldama were tried for treason, executed by firing squad and beheaded during the Mexican independence in 1811. Their heads were on display on the four corners of the Alhóndiga de Granaditas, in Guanajuato. During the Mexican Drug War, some Mexican drug cartels turned to decapitation and beheading of rival cartel members as a method of intimidation. This trend of beheading and publicly displaying the decapitated bodies was started by the Los Zetas, a criminal group composed by former Mexican special forces operators, trained in the infamous US Army School of the Americas, in torture techniques and psychological warfare. United States
The United States government has never employed beheading as a legal method of execution. However, beheading has sometimes been used in mutilations of the dead, particularly of black people like Nat Turner, who led a rebellion against slavery. When caught, he was publicly hanged, flayed, and beheaded. This was a technique used by many enslavers to discourage the "frequent bloody uprisings" that were carried out by "kidnapped Africans".