Rather than permit the Duke's heir, Frederick William, to succeed to his father's title, Napoleon seized the duchy and, in 1807, incorporated it into his newly created model Kingdom of Westphalia ruled by his brother Jérôme.

The dispossessed Frederick William, who had been a strenuous critic of French domination in Germany, seized this opportunity to seek Austrian help to raise an armed force.

William refused to accept this and led his Schwarze Schar ("Black Host") into Germany, succeeding in briefly taking control of the city of Brunswick.

Landing in England, the Duke was welcomed by his cousin and brother-in-law, the Prince Regent (later King George IV) and the Black Brunswickers entered British service.

However, steady attrition in battles and skirmishes through Portugal and Spain, combined with a lack of political support and financial difficulties, led to a situation where the unit's imminent disbandment looked likely.

[8] During this period, the Oels served in most of the major battles including Fuentes de Oñoro, Salamanca, Vitoria, the Pyrenees, Nivelle, the Nive, and Orthez.

[9] Following Napoleon's failed invasion of Russia in 1812, and his subsequent retreat back into France, William was able to return to Brunswick in 1813 to reclaim his title.

Upon Napoleon's escape from Elba in 1815 he once more placed himself under the Duke of Wellington's command and joined the allied forces of the Seventh Coalition in Belgium.

The sharpshooters of the Brunswick Advance Guard regiment were sent to support Dutch skirmishers in Bossou Wood on the allied right (western) flank; the rest of the corps took up a reserve position across the Brussels road.

Wellington moved the Brunswick infantry into the front line, where they were subjected to intense French artillery fire, forcing them to fall back a short distance.

[14] Wellington then ordered the Brunswick hussars to make an unsupported counterattack on the French light cavalry brigade, but they were driven off by heavy fire.

Later in the battle, French cuirassiers broke the allied front line and were only prevented from taking the crossroads by the Brunswick infantry who had formed themselves into squares.

[16] Only two days later, on Sunday 18 June, the Duke of Wellington positioned his Anglo-allied army along a ridge near the village of Waterloo, in order to block Napoleon's advance along the road to Brussels.

In the early part of the afternoon, the British Foot Guards moved down the slope to reinforce the Château d'Hougoumont, which was under fierce French attack; the Brunswick Corps was brought forward to take their place.

In all, 9,000 cavalry were involved in repeated attacks on the allied squares but were unable to break any of them, including the Brunswickers, who some British officers regarded as "shaky".

[18] The Brunswick hussars and uhlans, who formed part of the 7th British Cavalry Brigade, made harrying attacks on the French whenever they retired to regroup.

The French capture of the fortified farm of La Haye Sainte had left a gap in the centre of Wellington’s line, and the Brunswick infantry were brought along to fill it.

Faced with the veterans of the grenadiers of the Middle Guard, the inexperienced Brunswickers broke from the line and "fell back in disorder", but rallied when they reached the cavalry reserve in the rear.

[19][unreliable source] The Brunswick Corps had recovered sufficiently to participate in the allied “general advance” that swept the French army from the field.

Both units kept the skulls with the crossed bones on their helmets and caps and carried the battle honours "Peninsula-Sicily-Waterloo" until the end of World War I in 1918, when they were disbanded.

[34] The historic black of the Brunswick Corps was retained by the Husaren Regiment Nr.17 in full dress parade uniform until the outbreak of war in August 1914.