Trainbands (or Trained Bands) were companies of militia in England or the Americas, first organized in the 16th century and dissolved in the 18th. The term was used after this time to describe the London militia. In the early American colonies the trainband was the most basic tactical unit. However, no standard company size ever existed and variations were wide. As population grew these companies were organized into regiments to allow better management. But trainbands were not combat units. Generally, upon reaching a certain age a man was required to join the local trainband in which he received periodic training for the next couple of decades. In wartime military forces were formed by selecting men from trainbands on an individual basis and then forming them into a fighting unit.
London's long-established Trainbands often came into conflict with foreign mercenary companies that were hired by Thomas Wentworth, who sought to impose iron royal rule over England. However, Trained Bandsmen were basically inexperienced in contrast with professional soldiers who were veterans of the Thirty Years' War, and were no match for them in open conflict. In response, Wentworth had been careful to give the assignment of controlling London to mercenary companies whose soldiers were almost all Englishmen - many of them from the same plebeian neighborhoods in London that were the stronghold of the Trained Bands.
Trained Bandsmen were secretly hired by Richard Boyle through his ally Sir Paul Pindar to seem to threaten King Charles and his wife Henrietta Maria, in order to further discredit Wentworth. While the Bandsmen were no match for the mercenaries led by Captain Anthony Leebrick, their presence was enough to panic the queen, which provoked the horses pulling the king and queen's carriage to bolt, causing a crash which crippled the king and killed the queen.