How is Vanity Fair a historical novel?

Vanity Fair, written by William Makepeace Thackeray and published as a serial between 1847 and 1848, largely follows two female characters: Becky Sharpe, a poor orphan who seeks to obtain wealth through her cunning social maneuvers, and Amelia Sedley, born wealthy and engaged to Captain George Osbourne, who dies in the Battle of Waterloo.
Vanity Fair is a historical novel in that it satirically examines British society during and after the Napoleonic Wars. The novel's subtitle, "A Novel without a Hero," emphasizes the amoral, deeply flawed nature of its characters; their selfish, manipulative characterizations highlight the corruption and opportunism at the center of social life in Victorian England.
Further, Vanity Fair demonstrates how marriage often served as the primary vehicle for upward social mobility or financial security for women in Victorian England. Becky uses her romantic relationships for selfish gain, and both women find themselves in disastrous and loveless marriages. The novel, then, can also be understood as a critique of the commodification of women in marriage in Victorian England.
While the characters are engaging in manipulative, petty conflict, consumed by their own vanity and desire for enviable social stature, the Napoleonic Wars are waged in the background. This grave political conflict highlights the superficial aristocratic social conflict simultaneously occurring in England.
https://www.britannica.com/biography/William-Makepeace-Thackeray

https://www.telegraph.co.uk/books/what-to-read/why-vanity-fair-is-the-greatest-novel-about-waterloo/