The British Army during the American Revolutionary War served for eight years in campaigns fought around the globe. Defeat at the Siege of Yorktown to a combined Franco-US force ultimately led to the loss of the Thirteen Colonies in eastern North America, and the concluding Treaty of Paris deprived Britain of many of the gains achieved in the Seven Years' War. However several victories elsewhere meant that much of the British Empire remained intact.
In 1775 the British Army was a volunteer force that numbered just over 45,000 men thinly spread out in various locations globally. The army had suffered from lack of peacetime spending and ineffective recruitment in the decade since the Seven Years' War, circumstances which had left it in a dilapidated state at the outbreak of war in North America. To offset this the British government quickly hired contingents of German mercenaries to serve as auxiliaries alongside the regular army units in campaigns from 1776. Limited army impressment was also introduced in England and Scotland to bolster recruitment in 1778, however the practice proved too unpopular and was proscribed again in 1780.
The attrition of constant fighting, the inability of the Royal Navy to decisively defeat the French Navy, and the withdrawal of the majority of British forces from North America in 1778 ultimately led to the British army's defeat. The surrender of Cornwallis's army at Yorktown allowed the Whig opposition to gain a majority in parliament, and British operations were brought to an end.
Britain had incurred a large national debt fighting the Seven Years' War, during which the armies' establishment strength had been increased to an unprecedented size. With the ascension of peace in 1763 the army was dramatically reduced to a peacetime home establishment of just over 11,000 men, with a further 10,000 for the Irish establishment and 10,000 for the colonies. This meant 20 regiments of infantry totaling just over 11,000 men were stationed in England, 21 regiments were stationed in Ireland, 18 regiments were stationed in the Americas, and 7 regiments stationed in Gibraltar. Alongside this the army could call on 16 regiments of the cavalry, a total of 6,869 men and 2,712 men in the artillery. This gave a theoretical strength of just over 45,000 men exclusive of the artillery. The British government deemed this troop strength to be inadequate to prosecute an insurrection in the Americas, as well as deal with defence of the rest of its territories, so treaties with German states (mainly Hesse-Kassel and Brunswick) were negotiated for a further 18,000 men (half of which were stationed in garrisons to release regular British units from other theaters). This measure brought the Army’s total establishment strength to around 55,000 men.