Haydn's Missa in Angustiis (Mass in troubled times) was written near the end of the composer's life, in 1798. At this time, Napoleon Bonaparte's armies were having considerable success in their European campaigns and Austria was under threat.
In addition, because of the economic turmoil caused by this, Haydn's patron Prince Esterházy had recently dismissed the woodwind section of the court orchestra. As a result the scoring of the work was very sparse compared to other settings.
The work has a similar "darkness to light" structure to the 5th Symphony of Haydn's pupil Beethoven, written ten years later. It suggests a turning point in fortunes, and indeed in the year of its composition, the French fleet was destroyed by the Royal Navy in the Battle of the Nile, under the command of Lord Nelson. It is from this event that the soubriquet "Nelson Mass" is derived, though there is no evidence that Haydn himself ever described it as such.