It has been argued that one theme with respect to the military found in Pride and Prejudice concerns injustices among class distinctions within the military. This theme actually strongly connects with the book's central theme of prejudices concerning class distinctions, especially prejudices expressed by Mr. Bingley's sisters and Lady Catherine de Bourgh. As, W. A. Craik asserts in the book Jane Austen in Her Time, Austen was acutely aware of class distinctions that existed within the military. For example, the officers were given special privilege and treatment, even opportunities to attend balls while on active duty, but the mere foot soldiers were treated like what can be termed as "the scum of the earth" (found on p. 75, as cited in
"A private flogged," pemberley.com). Austen's reflection on the fact that soldiers were treated as an inferior class can be seen very, very briefly in Lydia's callous reference to the fact that "a private had been flogged" in Ch. 12, Vol. I. The theme of class prejudices among the military does reflects on the "great national event" of the rising middle class. At this point in history, new trade and developments were opening up new markets, giving the merchant class the opportunity to increase in wealth and giving rise to the middle class. Some of those among this new middle class were becoming wealthy enough to buy their own manor houses and rub shoulders with the established landed gentry. Mr. Bingley is an excellent example because his family's money and ability to rent an estate came from his family's trade business. Austen was well aware that this new historical rise in the middle class was also revealing the prejudices the classes felt towards each other, such as the noble class looking down on the middle class and even the new wealthy middle class looking down on the poorer merchant class, and it was these class prejudices that Austen used the book to expose, making class prejudices, like class prejudices among the military, a central theme.
Since Austen, being a social critic, was more interested in the social occurrences of her time, she focuses little on the "great national events" that would be considered political events; however, the fact that a regiment is stationed in Meryton is certainly a direct reflection on war between England and France. At the height of the French Revolution, particularly at the start of the "Reign of Terror" that ensued after Louis XVI was guillotined on January 21, 1793, France declared war on England and remained at war with England until 1802. The novel Pride and Prejudice was written in 1796, though published later, and reflects on some things that happened during that war period. For starters, it's interesting to note that England was not very prepared for a major war, particularly not after the country's losses during the American Revolution. Normally, those who could qualify for rank as officers had to be from the landowning gentry; however, the increased need for more members in the military and more officers meant that there was also a need to relax the requirements. In 1788, Jane Austen's own brother, Henry-Thomas Austen, who had been working towards being ordained as a minister at St. John's College of Oxford University, joined the Oxfordshire Militia Regiment and was given rank as an officer, despite being the son of a clergyman rather than a landholding gentleman. Henry-Thomas's socially and historically changing moment of being appointed an officer gave birth to Austen's antagonist George Wickham likewise being appointed an officer despite parentage ("Jane Austen & the Wars"). Hence, even George Wickham's character reflects on things going on within England's military during the historical war, more importantly, his appointment as an officer again reflects on the theme of class prejudices within the military and society at large.
The location of the militia in Meryton is also a direct reflection on the war between France and England. The area England would need to protect most would be London, which could easily be attacked by France via the English Channel. As a result, militia troops were positioned in areas surrounding London that could serve as speedy reinforcements should London indeed be attacked. Meryton is a village in Hertfordshire, and Hertfordshire is the county in which the book is mainly set. Hertfordshire is only roughly 26 miles north of London, so it makes perfect strategical sense for a militia to be stationed in Meryton with the purpose of defending London if needed. Hence, the reference to the fact that there is indeed a militia stationed in Meryton near Longbourn serves to illustrate the theme concerning life in England during wartime.