Why Britain's Parliament must still approve the army's very existence in peacetime
England once went to war with militias, noble retinues and hired foreigners, raising a proper force only for the length of a campaign. A civil war changed that, and the resentment left behind by Cromwell's troops explains why laws passed in 1689 still require parliamentary consent before the Crown can keep soldiers in peacetime.
Until the Wars of the Three Kingdoms, fought between 1639 and 1653, neither England nor Scotland had a permanent army led by career officers and sergeants. Expeditions such as Henry V's campaign to Agincourt in 1415 were staffed for the duration and then disbanded. During the civil war, Parliament decided that local militias could hold territory but not win, so it barred most of its members from serving as officers, Oliver Cromwell being the famous exception, and funded the New Model Army under Thomas Fairfax.
That force won, then became a political power in its own right and was widely disliked by 1660. When Charles II was restored that year it was paid off, and the king formed guards regiments at a cost of 122,000 pounds, the seed of a permanent English army. Numbers swung with events: 7,500 marching soldiers by 1685, a surge under James II after the Monmouth Rebellion, 94,000 under William III in 1694 and a nervous cut to 70,000 in 1697. The Bill of Rights and the Scottish Claim of Right, both of 1689, placed a standing army under parliamentary control.
The British Army proper dates from the 1707 union of England and Scotland, which merged the two armies; many of their regiments were already fighting side by side in the Netherlands in the War of the Spanish Succession. Seniority among the oldest line regiments follows the English order, which is why a Scots regiment raised in 1633 was ranked by when it reached England, and the Scots Greys ended up as the 2nd Dragoons.
Over the following centuries the army fought across the Seven Years' War, the Napoleonic Wars and the Crimean War, helped build an empire, and lost the Thirteen Colonies in the American Revolutionary War. At its 1813 peak the regular army topped 250,000 men, and Wellington and Blücher defeated Napoleon at Waterloo in 1815. Its soldiers still swear allegiance to the monarch as commander-in-chief.
Source: British Army
