With him, many have left Germany by railway (5)
I believe the answer is:
gerry
'with him many have left' is the definition.
The definition suggests a singular noun which matches the answer.
'germany by railway' is the wordplay.
'germany' becomes 'ger' (I've seen this in other clues).
'by' says to put letters next to each other.
'railway' becomes 'ry' (abbreviation for railway).
'ger'+'ry'='GERRY'
Can you help me to learn more?
(Other definitions for gerry that I've seen before include "-- Mulligan, US jazz saxophonist" , "- and the Pacemakers, 1960s pop group" .)