History of the Cannon

Background:

A cannon is a large tubular firearm that uses gunpowder aka. black powder to fire heavy or light projectiles over long distances. The cannon was first used in China and was a form of artillery (bombardment from a battery or large number of cannons) The cannon soon came to dominate warfare and lead us into the first gunpowder empires.

Post Medival Ages:

The end of the Middle Ages saw the construction of larger and more powerful cannon, and their spread in warfare throughout the world. The Tsar Pushka (Царь-пушка in Russian, literally "Tsar-cannon"), founded by Russian founding master Andrey Chokhov in 1586, was the largest howitzer ever made. The cannon, which still survives today, was intended to fire grapeshot and to defend the Kremlin, but was never used. In fact, with such a large cannon, it may have been intended as a showpiece of military might and engineering from the beginning

Modern Cannon:

The modern cannon generally refered to as a gun refers to a high velocity, low trajectory, direct fire weapon, such as the main gun on most modern main battle tanks.
Since World War II, the term has been used to refer to a gun of around 20 mm to 125 mm calibre, sometimes with an automatic loading action capable of firing explosive ammunition, an auto-cannon. (A howitzer typically means a weapon using a lower velocity than a cannon, which fires on a higher trajectory, and provides indirect fire.)
The minimum calibre of a cannon, 20 mm, has been a de facto standard since World War II, when heavy machine guns of 12.7 mm (0.5 inches) and 13.2 mm calibre were used side by side with 20 mm and larger guns, the latter using explosive ammunition (eg. RAF fighters with 20 mm Hispano cannon and Luftwaffe with 20 mm and 30 mm cannon). The Bofors 40 mm gun and Oerlikon 20 mm cannon are two examples largely used during World War II, and still in use today.