It was, of course, the unruliness, political ambitions and general dodgy behaviour of their knights that led so any monarchs in those times to rely on mercenaries, variously known as Free Lances, Condottieri or Gallowglasses. These were professional soldiers, well-disciplined and loyal as far as their contracts went. Many of them were specialists, such as the Genoese crossbowmen, Swiss halberdiers (who had a fearsome reputation), engineers, sappers and the owners and operators of the new-fangled, high-tech siege cannon.
Nowadays, of course, governments don’t employ mercenaries. Apart from the Popes’ Swiss Guard, of course. Oh, and the Brigade of Gurkhas.