Clue: Part of the Union in a right state (8)
Answer: ARKANSAS
Explanation: Definition: Part of the Union
A charade of 'a' plus R ('right') plus KANSAS ('state'). The definition is debatable: 'union' – no capital – could mean a group of states such as the USA, but with a capital generally refers (at least in the USA) to the Northern states in the Civil War. Arkansas did initially vote to stay in the Union, but then switched to the Confederacy.