Government concerned with eg uprising, arresting one million (6)
I believe the answer is:
regime
'government' is the definition.
(synonyms)
'concerned with eg uprising arresting one million' is the wordplay.
'concerned with' becomes 're' (re can mean regarding or about).
'uprising' is an anagram indicator.
'arresting' indicates putting letters inside.
'one million' becomes 'im' (resembles 1m).
'eg' is an anagram of 'ge'.
'ge' enclosing 'im' is 'gime'.
're'+'gime'='REGIME'
(Other definitions for regime that I've seen before include "Command" , "Ruling system" , "Method or system of government" , "Form of rule" , "Emigre (anag.)" .)