Military invasion refers to a large scale military attack by land, sea or air that aims to gain control over a territory that is not the invading force’s own. Invasions may involve the armed forces of one or more nations and can be accomplished by a number of methods that vary in their effectiveness.
The motivations for an invasion can include restoration of territory lost in the past; a desire to acquire natural resources such as water or petroleum; the pursuit of enemies; religious idealism; policies of colonization; and the quelling of destabilizing conflict within or between neighbors. Invasions can also be a means to change the leadership or political regime of a nation or region, though this is often controversial and frequently viewed as imperialism.
A successful invasion requires the occupying forces to establish good will with the people of the invaded country and create new habits that reflect respect for human rights. This is a difficult task, especially when the institutions of the previous government were repressive. For example, when the British attempted to capture the American city of Charleston, South Carolina in 1780, they ran into a defender at the Battle of Cowpens.
Invasions require a substantial amount of resources to be successful. This is especially true for a long-term occupation. For example, Operation Overlord in 1944 involved a massive assault from the sea and air by American, British, Australian and French armed forces. Each of these countries shipped a significant number of troops, supplies and equipment to England in advance of the invasion.