How Emacs recognizes the end of a sentence is controlled by the settings sentence-end-double-space and sentence-end. Controversy
Kaynak: Sentence spacing

19th century, style guides for writers began diverging from printer's manuals, indicating that writers should double-space between sentences.
Kaynak: Sentence spacing in language and style guides

will not break a line at a single space preceded by a period, but this behavior is configurable (with the option sentence-end-double-space).
Kaynak: Sentence spacing in digital media