Briefly, anybody who is in favour of the policies to expand the territory of the land/state he/she belongs to is a pro-expansionist person....
Yes they were expansionists.
Expansionist
James K Polk
"To what extent should nations respond with diplomacy to the expansionist policies of other states?"
No, he was not, he was an uneducated dictator.
Expansionist
Japan
being the first deliberate expansionist
A pro-expansionist is someone who supports and advocates for the expansion of territories, influence, or domains, often through political or military means. They believe in increasing the reach and control of their country or group.
Manchuria
Hitler
I don't know .