IPA: /ˌænɛkˈseɪʃənɪst/
KK: /æˈnɛkseɪʃənɪst/
A person who supports or promotes the act of annexing, which means adding territory to a country or state.
The annexationist argued for the benefits of expanding the nation's borders.
Annexationist is formed from "annex" (from Latin "annexare", meaning to attach or join) and "-ion" (meaning the act of) combined with "-ist" (meaning a person who). The term describes a person who advocates for the act of annexing or joining territory.
Think of someone who is involved in the 'act of joining' ('annex') land or territory, and the '-ist' indicates they are a person who supports this action.