invader
n.a person or group that enters a country or area without permission, usually to take control or cause trouble. You use this word when someone is attacking or taking over a place.
n.a person or group that enters a country or territory without authorization, typically with the intent to seize control or cause disruption. Often carries a political or military connotation.
“The army fought hard to stop the enemy invader.”
“The local community organized a protest to welcome the peaceful invader and ensure their safety.”
“Historians often debate whether the group was a legitimate refugee seeking asylum or a foreign invader seeking to exploit the region's natural resources.”
“Among the most important immune cells involved in fighting such invaders are neutrophils.”
From invade + -er.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.