The Napoleonic Wars are not directly mentioned in Pride and Prejudice. However, this historical period does play a part in the novel, since it is the reason why there are soldiers stationed in Meryton and then Brighton.
Good Heaven! Brighton, and a whole campful of soldiers, to us, who have been overset already by one poor regiment of militia, and the monthly balls of Meryton!
Austen does not pay homage to the war as much as to the soldiers, and their immediate effect on the society girls who mingled with them. Remember that, rather than a historical fiction novel, Pride and Prejudice deals strictly with the "universally acknowledged" obligation of men who have come to property to get a wife; similarly, Austen depicts the dynamics of the females who are the object of the attention of such men. Hence, the addition of the soldiers not only acknowledges the reality that Austen, herself, experienced in her surroundings, but it also allows for the addition of character such as Wickham and his fellow commissioned officers who--most of them--were gentlemen with good intentions who rightly revelled in the attentions they could pay to the socially receptive ladies.
Adding the troops to the novel also works effectively to add Lydia's elopement with Wickham to the plot. Lydia, who is air-headed, superficial, and obsessed with the soldiers and their lifestyles, is the perfect character to complicate matters between Darcy and Elizabeth. Additionally, the use of the soldiers allows Elizabeth to establish a friendship with Wickham, develop a little crush on him and, in the process, discover both versions of the Wickham tales regarding the Darcy's.
One more thing that connects the war to the plot is the "landed gentry" that surfaces, not through aristocracy (like the Darcy's), but through trades and other newer ways of making money that came as a result of the war. It is known that, when one is victorious during a war (England was victorious over the French and Napoleon), money flows in. Additionally, the Industrial Revolution that took over England made it one of the richest nations in the world which, by default, meant that the middle class became strengthened and richer, like the Bingley's father. This element is also effective in the plot, as it allows Caroline Bingley to have a sense of superiority over Elizabeth and Jane, who represent long-established wealth and gentry (though Bennet squandered his wealth) and to feel equality with Miss Darcy, who represents long-established aristocracy and great wealth.
Therefore, it is safe to argue that though the Napoleonic Wars themselves were not included directly into the narrative, the influx of soldiers and wealth into the social lives of young ladies of a marriageable age was noted as important to society and effective for the plot.