Mechanized warfare
It was decided therefore to slow the production of the U.S. heavy tank designs such as the M26 Pershing and concentrate resources on mass-producing the M4 Sherman and tank destroyers such as the M18 Hellcat.
To be able get into position to counter-attack, the tank destroyers had to be fast. To achieve the desired mobility and agility from the engines available the armour protection was sacrificed, a measure of protection coming from being nimble and hopefully from being able to knock out the enemy before they could get a shot in. Although they usually had guns of either 75 mm or 76 mm calibre (the M36 used a 90mm calibre gun), the tank destroyer units were issued with the ancestor of the modern armour-piercing discarding sabot, rounds which made their guns much more powerful than a simple comparison of calibres would suggest.

Japan: The Japanese doctrine was mainly French in concept but with some purely Japanese elements. Due to Japan's naval priorities in warship construction and inter-service feuds (the marine branch of the IJN favoured all-around protective armour) IJA tanks were lightly armoured. As with most armour during the 1930s, the main guns were small in calibre: 37 mm for their Type 95 light tanks and 47 mm for the Type 97 medium tank, but this was sometimes compensated by a high muzzle velocity. The IJA's use of tanks in China exemplifies its doctrine: light tanks were used for scouting or acted as mobile infantry support, while medium tanks supported the infantry and assaulted deeper objectives, but did not fight en masse.
In 1939, the Japanese Army engaged Soviet armour at Nomonhan. During the three-month-long war, Japanese armour had shown their weakness against Soviet tanks; and the resulting Japanese defeat prompted a series of complaints by the Imperial Army to incorporate improvements in future Japanese armour. This is the primary reason IJA tanks were not as successful while being used with IJA tactics. The tank forces of the U.S. Army consisted of the M2A4 and M3 Stuart light tanks up until 1941, although these vehicles were five years newer than the 1935 built Type 95's, the IJA and U.S. light tanks were comparable to each other, and seemingly performed well for their respective forces during jungle combat operations; during their phase of World War II.
As with all armour, maintenance was a continuous challenge; especially in tropical environments. When IJA and SNLF (Imperial marines) tanks did clash with the enemy they were quickly destroyed by concealed anti-tank guns or overwhelming numbers of hostile tanks. Japan was a naval power, and concentrated its production on warships, thus placing a low priority on armoured vehicle development, its tanks becoming quickly obsolete during the later years of the war. A number of designs that were equal to heavier foreign types were on the drawing board at the beginning of the war, but would only be built in small numbers towards the end, being placed in reserve, to be deployed for the defence of Japan itself.

China: The Republic of China's National Revolutionary Army's 200th Division was the country's only mechanised division during the war. The 200th used pre-war tanks acquired from Italy, Germany, and the Soviet Union.

After 1945: 

Indo-Pakistani wars: 

Arab–Israeli wars: The conflict between Arab nations in the East Mediterranean region and Israel in particular would serve to become a testing ground for development in armoured warfare during the decades of the Cold War. Both sides in the Arab–Israeli series of conflicts made heavy use of tanks and other armoured vehicles due to the practicality of tanks in the desert environment these conflicts largely took place in.
During the 1956 Suez War and Six-Day War (1967), Israeli armoured units typically had the advantage, mainly due to good tactics and unit cohesion.
Conversely, the Yom Kippur War (1973) illustrated the problems that can arise if armoured and infantry units do not work closely together. Israeli tanks, operating independently in large numbers, were decimated by Egyptian anti-tank teams, well-distributed amongst regular infantry, and often equipped with new, first-generation portable anti-tank guided missiles. This is an extreme example but exemplifies what has been fairly thoroughly documented since the Second World War: tanks and infantry work best by taking advantage of each other's strengths and combining to minimise the weaknesses.
In many conflicts, it was usual to see infantry riding on the back of tanks, ready to jump off and provide support when necessary. Unfortunately, the design of many modern tanks makes this a dangerous practice. The turboshaft-powered M1 Abrams, for example, has such hot exhaust gas that nearby infantry have to be careful where they stand. Tanks can also be very vulnerable to well aimed artillery; well-coordinated air support and counter-battery artillery units can help overcome this.

Emergence of guided missiles: While attempts to defeat the tank were made before and during the Second World War, through the use of conventional high velocity anti-tank artillery, this proved increasingly difficult in the post-war period due to increased armour protection and mobility of tanks.
In response, the Soviet Union, the country with the largest armoured fleet in the world, strove to incorporate some anti-tank capability into almost every infantry weapon. By the 1960s, Soviet defense scientists were designing portable anti-tank guided missiles. These new weapons were to be either carried by infantry, or fired from the newly developed BMP-1 infantry fighting vehicle. They were in use with Soviet forces before the end of the decade.
In 1973, the Israeli Army failed to anticipate the importance of these new weapon systems. Hundreds of AT-3 Sagger man-portable anti-tank guided missiles (ATGMs), supplied to Egypt by the Soviet Union and could be operated by infantry without having extensive training, inflicted heavy losses on the Israeli armoured formations. Since then, ATGMs have played an important role within the Israeli Army, having developed advanced domestic-made versions (see Spike/Gil missile), which have been widely exported throughout the world.
In the recent 2006 conflict with Hezbollah, while Israeli infantry were able to easily defeat opposing ATGM teams, tanks operating on their own suffered several hits from the latest advanced Russian tandem-warhead types (such as the Kornet). This highlighted that tanks operating solely, in the era of ATGMs, are extremely vulnerable.
Responding to the serious tank losses suffered against Hezbollah, Rafael Advanced Defense Systems in cooperation with Israel Aircraft Industries developed a missile defence system for tanks, called Trophy, to intercept and destroy anti tank missiles. The system was successfully deployed in combat on March 1, 2011, when it intercepted an anti tank missile during an engagement on the Gaza border.

NATO: During the Cold War, NATO assumed armoured warfare to be a dominant aspect of conventional ground warfare in Europe. Although the use of light tanks was largely discontinued, and heavy tanks were also mostly abandoned, the medium tank design evolved into heavier models due to increase in armour and larger sized main weapon resulting in the main battle tank (MBT) which came into existence, combining most of the different types of tanks during World War II.
For the most part the NATO armoured doctrine remained defensive, and dominated by use of nuclear weapons as deterrence. Although most NATO nations began the Cold War period with a large number of U.S.-designed tanks in their fleets, there was a considerable degree of disagreement on the design of future MBTs among the NATO major nations. Both the U.S. and Germany experimented with, but abandoned the missile-armed MBT-70. The M26 Pershing basic design of the United States would evolve until the M60 main battle tank was replaced with the gas-turbine powered M1 Abrams in the 1980s. The British Army also retained a World War II tank design, the Centurion, which proved to be highly successful and was not fully replaced until the 1970s.
The West German Bundeswehr decided to develop their own tank in the 1960s, and in the 1970s produced the Leopard I, which was a somewhat lighter design, conforming to German doctrine that emphasised speed over protection. From the same initial collaborative project as the Leopard I, the French series of AMX tanks also emphasised manoeuvre over protection. By the 21st century, most advanced western main battle tanks were built around powerful engines, large 120 mm guns and composite armour.

Warsaw Pact: The Warsaw Pact armoured doctrine was substantially influenced by the developments in the Soviet Army which sought to adopt its existing doctrine evolved during World War II to the nuclear battlefield. In the early 1960s this led to a number of important developments in the armoured forces and their supporting Arms. One important development was the transition of the Second World War use of Cavalry-Mechanised Group (CMG) into the Cold War Operational Manoeuvre Group (OMG) that was designed to exploit breakthroughs to penetrate NATO's defences in depth. This was a culmination of the Deep Battle theory dating to the 1930s.
In 1964 a significant breakthrough in tank design was achieved in the Soviet Union when the T-64 was produced which for the first time used an automatic loader, reducing the crew of the tank to three crewmen. Subsequently, this model, and the later T-72 and T-80 tanks introduced further innovations that influenced armoured warfare by introducing guided missiles into the tank ammunition mix, allowing ATGW fire from standard tank guns.