An invasion force refers to a group of individuals or soldiers who enter a foreign land without permission or in an aggressive manner. Some of the synonyms for invasion force include the following: 1) raiding party, 2) strike force, 3) assault team, 4) invasion unit, 5) aggressive force, 6) attack squad, and 7) occupation troops. These synonyms are commonly used in military and political contexts and can convey a sense of force and aggression towards a particular group or nation. It is important to note that these terms should be used with caution, as they may evoke negative connotations or represent acts of violence and aggression.