The battles of the Great French War (1792-1815), which was the period of almost constant warfare that included the Napoleonic wars, were infantry battles. When the Duke of Wellington defeated Napoleon Bonaparte at the Battle of Waterloo, the French army consisted of 69,000 men, while the Allied forces consisted of a British army of 67,000 and a Prussian army of 48,000.
Things began to change in the Crimean War (1853-1856) against Russia. British and French forces landed in the Crimea, but found difficulty in trying to capture the Russian town of Sevastopol:
The invention of the Gatling machine gun in 1861 changed battles in favour of the defence – attackers on foot could be killed faster than they could charge. It was used in the American Civil War (1861-1865) and the Franco-Prussian War of 1870-1871.
The strength of the Royal Navy meant that it was difficult for Britain to be invaded. This was a major factor in Britain's world power:
After the wars with Napoleon, the nations of Europe developed the Congress System – a series of regular meetings to resolve problems and put down rebellions.
In 1859, a Swiss businessman called Henri Dunant witnessed the battle of Solferino. He was so horrified that he helped to set up the Red Cross (1863) and organised an international conference that agreed the first Geneva Convention (1864).