Invasions are large scale military operations that can have significant consequences for the areas and people involved. These impacts can range from a loss of life to the growth of an empire.
The basic difference between Occupation and Invasion is that the latter starts outside of the country, and a physical movement of troops, vehicles, material and equipment into the enemy country must take place (think D-Day). Invasion is accompanied by fighting to destroy or capture enemy forces, strong points and critical infrastructure.
For this reason, a military invasion usually requires substantial preparation. Leaders must be able to effectively communicate their intentions and tactics to their troops. This can be done with written or verbal commands, as well as in person. For example, Alexander the Great led his armies personally to ensure that all his orders were carried out. Custer, on the other hand, ignored orders to wait for Brigadier General Alfred Terry and Colonel John Gibson’s troops to arrive before he attacked the Sioux and Cheyenne at the Battle of the Little Bighorn.
Military invasion is one of the most complex forms of warfare, requiring significant resources and planning. There are a number of different methods of attack, including a pincer movement (attacking two sides at opposite locations) or a bull horn formation (attacking three areas at once, often cutting off retreat and additional support in preparation for total annihilation).
Regardless of their intended objectives, all invasions carry with them a certain degree of risk and the possibility of failure. Nevertheless, invasions can also change the world map, as they have for centuries.