The Battle of Waterloo was fought near the town of Waterloo, Belgium (then the Netherlands). Napoleon led his battered French Army (73,000 men) against the combined might if the British Army led by the Duke of Wellington and a Prussian Army led by General von Blücher (118,000 men combined/ 31,000 Brits, 50,000 Prussians, 17,000 Dutch, 20,000 Hannover/Nassau/Brunswick men). The Brits and Germans were going to be reinforced by Russian and Austrian troops soon bringing the entire Seventh Coalition to bear against Napoleon's force. Napoleon hoped to go on the offensive, smashing the British and Germans, and destroy the Russians and Austrians piecemeal. Thing is, he almost beat the Coalition at Waterloo too.
Before the battle the Prussians were beaten at Lingy and Wellington was fought to a stalemate at Quatre Bras; however, with the Prussians pulling back Wellington was forced to do the same. Napoleon sent a part of his force to chase off the Prussians while his main force crushed Wellington, now camped around Waterloo. However, the Prussian rearguard tied down their French pursuers at Wavre. This allowed the rest of the Prussian Army to move to reinforce Wellington. Wellington meanwhile was having an increasingly hard time beating back the French attacking his men at the Mont-Saint-Jean escarpment. However the increasing number of arriving Prussians eventually put an end to French assaults, which were followed by Allied attacks. The Prussians quickly broke the French right and the rest of the French army soon followed suit. Napoleon retreated leaving 26,000 men dead on the field with an additional 15000 wounded. The Allies had it a lot better, losing only about 24000 or so if I remember correctly.
The loss was a tremendous blow, ending any remote hope of Napoleon fending off the Seventh Coalition. With British and Prussian forces consolidated and Russian and Austrian reinforcements on the way the writing was on the wall, Napoleon abdicated 4 days later on June 22nd, 1815. The Seventh Coalition took Paris on July 7th and the French Empire was brought to an end. Napoleon would die some years later in exile on the tiny island of St Helena. Meanwhile, Europe entered a period of relative peace, until the German Wars of Unification.
