Final answer:
A synonym for incursion is 'invasion,' which is another term for an aggressive entry into another's territory with the intent to conquer or occupy.
Step-by-step explanation:
A synonym for incursion, which means an attack on another's territory, is invasion. This term is often used in the context of military action where one nation penetrates another's borders with the intent to conquer or occupy. Other related terms that describe similar concepts include conquest, which refers to the act or process of conquering, and annexation, a political action where a nation or other political entity declares sovereignty over an area previously outside its borders.