Napoleon Bonaparte had already succeeded in eliminating most of those who would oppose his pan-European vision.
Victories over Prussia, Russia and Austria left only Britain to prevent the French from taking over completely.
Although Nelson´s victory at Trafalgar, off the coast of south-west Spain meant that Britain was safe from invasion (Napoleon was however planning to dig a tunnel under the English channel!), his relentless march into other European lands threatened British interests and the balance of power in Europe.
Napoleon´s invasion of Spain in 1807, and his deposing of the king in favour of putting his brother Joseph on the throne of Spain was resisted by the Spanish. The angry reaction of the Spanish people encouraged Britain to send in an expeditionary force. Napoleon had underestimated the strength of feeling among the Spanish, and although expecting a rebellion of sorts, did not think that it could not be easily
Lieutenant-General Wellesley landed in Portugal in 1808 and after a few skirmishes, established a defensive position to enable reinforcements to arrive. Napoleon´s armies, led by Junot attacked, and for the first time, were defeated, thanks to the defensive tactics employed by Wellesley´s army.
Any great opportunity to inflict a quick defeat on the French was lost as Burrard and then Dalrymple, both outranking Wellesley, replaced him as commander-in-chief. The French did however decide to evacuate from Portugese soil under the controversial Sintra Agreement.
Sir John Moore took control as the previous three returned to Britain to face criticism. The Peninsular War escalated still further with the Spanish gaining victory over Dupont´s forces, provoking the arrival in Spain by Napoleon himself, along with a force of 200,000 veteran soldiers.
Moore advanced towards Burgos in order to draw French troops away from southern Spain, but was forced to retreat further and further westwards, culminating in the evacuation of his army from La Coruña and the loss of Moore´s life.
Wellesley returned to Iberia and took control once again, having been absolved of the criticism surrounding the Sintra Agreement. Napoleon had already returned to France and transferred control to Soult, once the Moore retreat was underway.
Re-organising his army to include a company of riflemen within each division, and the incorporation of a battalion of Portugese Infantry into each brigade, they crossed into Spain in May, and joined forces with the Spanish army.
Fortunes swung back and forth over the next year, with the Spanish suffering heavy defeats, and the British/Portugese having to retreat to protect supply lines. Wellesley, by now Viscount Wellington of Talavera began to prepare defensive postitions around Lisbon. These defensive lines proved to be vital as Massena and the French attacked, and forced Wellington back behind the lines in an attempt to retake Portugal. Only the imminent arrival of British reinforcements prevented Massena from administering the coup de grace.
With one French army under Soult checked by Graham's victory at Barrosa on 5th March 1811, Wellington was able to push Masséna out of Portugal. Counter-attacks at Fuentes de Oñoro on 3rd and 5th May 1811 were repulsed after desperate struggles in the streets of the village. Masséna, having failed to re-take Portugal, was replaced by Marmont.
A further bloody battle took place at Albuera on 16th May as Soult's move north was intercepted by a combined British-Portuguese-Spanish force under Beresford. Although Beresford's handling of the battle - in which the French made the largest single infantry attack of the War - attracted much criticism, Soult was finally forced to retreat.
French armies continued to threaten Wellington throughout the latter months of 1811, but at no time were able to catch him at a disadvantage. The turning point of the war had been reached.
During January 1812, Wellington´s forces moved eastwards despite facing a numerically superior force. This was achieved thanks to the Spanish, moving in small groups, utilizing guerrilla tactics and pinning down French forces, preventing them from reinforcing the front line. By August, Wellington had entered Madrid. Soult continued to fight back and pushed Wellington´s forces into a retreat from Burgos into Salamancar, and then back further into Cuidad Rodrigo.
Napoleon´s Russian adventure in 1812 had ended in disaster, and French forces had been pushed back to the Elbe River. This allowed Prussia to re-enter the war, meaning that Napoleon was unable to send reinforcements to the Iberian Peninsula. Wellington however was receiving huge numbers of reinforcements.
Wellington pushed forwards and the decisive battle of the war was at Vitoria, where French General Joseph saw his army decimated in the valley of the Zadorra River.
Buoyed by Wellington´s victories, Prussian and Russian forces, although having suffered several defeats, regrouped and attacked from the east, to be joined by the Austrians.
By July 1813, Wellington reached the Pyrenees, and by October had entered France. Napoleon´s army of 300,000 men had been defeated by 40,000 British troops. This was mainly because the Spanish tactics meant that France was never able to commit more than 70,000 men to the fight against Wellington, 230,000 being needed to maintain control over the unruly Spanish.