Question: La Haye farm was one of the most fortified garrisoned points during which battle fought in present-day Belgium on Sunday, 18 June 1815?

Context paragraphs:
9th Light Infantry Regiment: The 9th Light Infantry Regiment (9e régiment d’infanterie légère) was a French army regiment.  One of the most notable infantry regiments in the Napoleonic Wars, it was awarded the title "Incomparable" by Napoleon Bonaparte after their brilliant performance at the Battle of Marengo on 14 June 1800.  The regiment went on to serve with distinction in the [Ulm Campaign], at the Battle of Dürenstein (11 November 1805), the Jena Campaign (1806), and the Battle of Friedland (14 June 1807).  The regiment then served in the Peninsular War taking a notable role at the Battle of Talavera 27–28 July 1809 and the Siege of Badajoz (1812).  Battalions from the regiment also fought on the Wagram Campaign (1809), at the Battle of Leipzig (16–19 October 1813), and Napoleon’s campaigns in France (1814).  During the Hundred Days the 9th Light fought at Battle of Ligny (16 June 1815) and the Battle of Wavre (18–19 June 1815).  The regiment was disbanded in the aftermath of the Bourbon Restoration.

La Haye Sainte: La Haye Sainte (named either after Jesus Christ's crown of thorns or a bramble hedge round a field nearby ) is a walled farmhouse compound at the foot of an escarpment on the Charleroi-Brussels road in Belgium.  It has changed very little since it played a crucial part in the Battle of Waterloo on 18 June 1815.

Battle of Ligny: The Battle of Ligny (16 June 1815) was the last victory of the military career of Napoleon Bonaparte.  In this battle, French troops of the Armée du Nord under Napoleon's command, defeated part of a Prussian army under Field Marshal Prince Blücher, near Ligny in present-day Belgium.  The Battle of Ligny is an example of a tactical win and a strategic loss for the French.  While the French troops did force the enemy to retreat, the Prussian army survived and went on to play a pivotal role two days later at the Battle of Waterloo, reinforced by IV Prussian corps that had not participated in the battle at Ligny.  Had the French army succeeded in keeping the Prussian army from joining the Anglo-allied Army under Wellington at Waterloo, Napoleon might have won the Waterloo Campaign.

Battle of Waterloo: The Battle of Waterloo was fought on Sunday, 18 June 1815, near Waterloo in present-day Belgium, then part of the United Kingdom of the Netherlands.  A French army under the command of Napoleon Bonaparte was defeated by two of the armies of the Seventh Coalition: a British-led Allied army under the command of the Duke of Wellington, and a Prussian army under the command of Gebhard Leberecht von Blücher, Prince of Wahlstatt.

De La Haye scandal: The De La Haye scandal was a major scandal which took place in 1919 in the city of Madras (now known as Chennai), India.  It resulted in the murder of De La Haye, the principal of Newington House, a college in Madras on the night of 15 October 1919 and a highly sensationalized trial known as the De La Haye murder case or Madras murder case.  No one was implicated and the case remains unsolved to this day.

John Lucie Blackman: John Lucie Blackman (4 October 179318 June 1815) was a British soldier who fought in the Peninsular War and was killed at the Battle of Waterloo on 18June 1815 aged 21.

Waterloo Medal: It was announced in the London Gazette on 23 April 1816 that in a memorandum from Horse Guards on 10 March 1816 by the Prince Regent that The Waterloo Medal was conferred upon every officer, non-commissioned officer and soldier of the British Army (including members of the King's German Legion) who took part in one or more of the following battles: Battle of Ligny (16 June 1815), Battle of Quatre Bras (16 June 1815), and the Battle of Waterloo (18 June 1815).

Christian Friedrich Wilhelm von Ompteda: Christian Friedrich Wilhelm Freiherr von Ompteda (26 November 1765, Ahlden an der Aller - 18 June 1815, La Haye Sainte) was a Hanoverian officer of the Napoleonic Wars.

Samuel Ferrior: Samuel Ferrior (177218 June 1815) was a British soldier killed at the Battle of Waterloo on 18June 1815.

La Haye, Lasne: La Haye was a farm, in a hamlet of the same name, in the Belgian municipality of Lasne.  It was destroyed by fire in 1910.  During the Battle of Waterloo (18 June 1815) the farm was one of the fortified garrisoned points that made up a bulwark on the extreme left (eastern end) of the Duke of Wellington's Anglo-allied line.

Supporting paragraphs: La Haye, Lasne Battle of Waterloo
Answer: Battle of Waterloo