Military offensive in which large numbers of combatants of one geopolitical entity enter territory owned by another such entity
An invasion is a military offensive of combatants of one geopolitical entity, usually in large numbers, entering territory controlled by another similar entity. Generally, invasions have objectives of conquering, liberating or reestablishing control or authority over a territory; forcing the partition of a country; altering the established government or gaining concessions from said government; or... Wikipedia