author
Little is known about the person behind this byline, which adds a bit of mystery to the work. The name appears to have been used as a simple author credit for a 19th-century military and political history of the Crimean War era.
by A British officer
Project Gutenberg and The Online Books Page list A British officer as the author credit for The Powers of Europe and Fall of Sebastopol. In the available catalog records, that wording appears as a byline rather than a clearly identified personal name.
Because the author is presented under a generic description instead of a full name, reliable biographical details are hard to confirm. Based on the title and attribution alone, this seems to be an anonymous or pseudonymous military writer whose perspective was connected to British service life and mid-19th-century European affairs.
No trustworthy source reviewed here provided a verified real name, life dates, or a confirmed portrait, so it is best to treat this author as effectively anonymous.