Under threat of invasion by the French Revolutionary government from 1793, and with insufficient military forces to repulse such an attack, the British government under William Pitt the Younger decided in 1794 to increase the Militia and to form corps of volunteers for the defence of the country.
[1] Despite the end of the Napoleonic Wars in 1815, the Yeomanry was retained by the government "for Military Service in aid of the Civil Power" in the absence of organised police forces.
[2] The Yeomanry was not intended to serve overseas, but due to the string of defeats during Black Week in December 1899, the British government realized they were going to need more troops than just the regular army.
[3] In the aftermath of the war, a number of new regiments were formed and Haldane's Reforms resulted in a more effective reserve force for home defence.
Indeed, by the end of the war, just 17 1st Line regiments remained as mounted cavalry; the rest had been converted to infantry or machine gun battalions.