If you describe something as ephemeral, you mean that it lasts only for a very short time. He talked about the country's ephemeral unity being shattered by the defeat = transient. existing or popular for only a short time (ephemeros , from hemera )
Short-lived; existing or continuing for a short time only Many small upland streams in the HBEF are ephemeral, flowing only after snowmelt or particularly heavy storm events
\ih-FEM-er-ul\, adjective: 1 Beginning and ending in a day; existing only, or no longer than, a day; as, an ephemeral flower 2 Short-lived; existing or continuing for a short time only
enduring a very short time; "the ephemeral joys of childhood"; "a passing fancy"; "youth's transient beauty"; "love is transitory but at is eternal"; "fugacious blossoms"