Invasion refers to a large-scale military operation in which the armed forces of one geopolitical entity enter another territory with the intent of conquest or occupation. This can occur within the framework of a war or as an independent conflict. Invasions typically result in the reshaping of the culture and political landscape of the invaded nation.
Invasions may be carried out by land, sea, or air, with each method having arguments both in favour of and against it. Invasion by air usually entails the use of aircraft to transport troops into the target country, or it may involve the dropping of troops from an aircraft. In the past, invasions by sea or land were often accompanied by other forms of attack on the target in order to “soften up” the country and deprive it of resources; such preparations have been referred to as an act of preemption.
Land-based invasions have been used since the invention of warfare, often involving a straightforward crossing of borders or other demarcated zones. Invasion by land can be complicated by the existence of defensive emplacements and structures, which can prove difficult to overcome. Communication between the invaders and defenders has historically been crucial, and the development of voice or morse code communication has allowed even small units of skirmishers to relay defensive positions to their commanders.
Arguments in favour of an invasion by sea usually include the ability to perform a surprise attack from sea, or that the defences of the target nation are insufficient to repel such an attack. The logistical problems associated with this form of invasion, however, have made it a rare form of invasion.