A Military invasion is the act of sending armed forces into another territory with the intention of capturing it and imposing a new regime or occupying the area. There are several different methods of invasion, each with arguments both in favour and against it. These include invasion by land, sea or air.
Invasions are typically large-scale operations, requiring a substantial force to be successful. This is because, in general, the greater the area of territory that needs to be defended, the more difficult it is to control, given the size of the required military force. This is especially true if the terrain is inhospitable or difficult to traverse, such as mountainous areas or dense forests.
The most common method of invasion is by land, with soldiers entering through a border crossing or port. Alternatively, a series of forts can be constructed in the form of a barrier along a country’s border. These fortresses are usually spaced apart, allowing defenders to intercept invader supply lines. This is the concept behind the Maginot Line.
Invasions are usually mounted for the purpose of achieving some sort of political, military or economic objective. These goals might include restoration of a lost territorial base; pursuit of enemies; acquisition of natural resources, including natural gas; quelling destabilizing conflict within or between nations; or punishment for a perceived slight. Invasions are normally mounted for straightforward military and geopolitical gain, although there have also been numerous justifications advanced by the invaders themselves.