the.com/beginning of the end

means The point at which a failure, loss, or downfall first becomes noticeable, even though its causes had already been set in motion earlier.

from A phrase rather than a single coined word, it entered wide circulation through Talleyrand's reported remark about Napoleon's position after a military setback — 'the beginning of the end.' Whether or not he actually said it, the line stuck, and the phrase spread through 19th-century political and military writing before settling into everyday use for any visible first crack in something that's doomed to collapse.