Military Invasion
A Military invasion is when a group of armed forces from one geopolitical entity enters territory that is controlled by another. Invasions can be part of a larger war or may be an independent conflict. They typically result in occupation of the invaded territory and can profoundly change the culture and politics of that region. A major goal of an invasion is the pacification (subduing) of the occupied country. This can be difficult and time consuming. It usually involves a change in government, and may include restrictions on the activities of political groups like opposition parties or religious leaders. It can also involve requiring a paying of reparations or tribute to the invader.
The most common method of invasion is by land. It involves marching a large number of troops into the target region, often crossing borders or special areas that are off limits to military activity (like a demilitarized zone). This is a slow way to get into an area, and it is hard to keep secrets about it. It is also hard to get supplies to troops after they land. A newer method of invasion involves sending armed forces in aircraft. They can land, or jump out using parachutes. This can be faster than a land or sea invasion, but it is still hard to keep secret.
Invasions have been a frequent occurrence since antiquity, when they were often used to conquer and colonize the world. They have also been used to spread ideas, such as religion or philosophy, and to bring technology into new environments. In modern times, it has been a growing trend to euphemistically label invasions as interventions. This is likely motivated by a desire to avoid accusations of imperialism.