But there's another major factor that kept the tank going for so long; the Cold War arms race. Russia saw the tank as their principal land warfare weapon and produced over 100,000 of them after World War II. Russia introduced a new model every decade from 1945 to the 1990s. The World War II T-34 gave way to the T-54, then the T-62, the T-72, the T-80 and the T-90. The United States responded with the M-48, M-60 and M-1.
As the Arab-Israeli wars, and the 1991 Gulf War demonstrated, the American tanks in the hands of well trained crews could handily defeat larger numbers of Russian tanks. But the M-1, with it's use of high tech sensors, composite armor and depleted uranium shells, set a new standard for tank design and effectiveness. It also cost nearly five million dollars each. With Russia dropping out of the arms race when the Soviet Union collapsed in 1991, and no one else willing, or able, to afford a tank to match the M-1, the end of the line has been reached. Well, a few nations could match the M-1 (Israel, Britain and Germany), but none of these were willing to build many of them.
The United States ended up with 7,000 M-1s when the Cold War ended. Russia was selling off its best tanks for less than a million dollars each, but no one thought of these as anything more than targets in a battle with M-1s. The world will still have plenty of tanks for the next few decades, until the last of the 50,000 Cold War surplus Russian tanks rusts into uselessness.
But why should the tank disappear now? Simply because the main reason for the tank was to provide a weapon that could battle its way past determined infantry and their machine-guns, artillery and anti-tank weapons. With modern electronics, cheaper precision rockets and bombs can deliver the firepower and flexibility that only tanks could provide in the past. These new weapons are easier to use and maintain than tanks, which have always been complex and difficult to keep going. Just like admirals did the math and decided that submarines and aircraft were cheaper and more effective than battleships, generals the world over will consider their options and go with what they feel will work best. There won't be much choice. With few new tanks being built, and cheaper, more effective, weapons available.
There will have to be some battles to make the point. China and India are still building tanks, using technology far behind, and a lot cheaper than, the M-1. But with smarter and cheaper anti-tank weapons available (missiles, "smart mines" and air delivered robot tank killers like SADARM), it will only take one incident of the "cheap and smart" stuff beating up on a lot of tanks to make the point. Another telling sign is the lack of enthusiasm in America and Russia for designing a replacement for current tanks. At least not a replacement that features the "bigger gun and thicker armor" that has characterized tank development for the past 80 years.
Then again, it may be premature to write off the tank. For a weapon that has been dismissed as obsolete for decades, it still survives. True, there are a lot fewer tanks in use now (about 60,000) than there were at the end of the Cold War (over 100,000). And the new ones being built are not sufficient to replace those that wear out each year. Less affluent nations will still find tanks useful against their own citizens, or equally poor neighbors who also have some tanks. The math, however, is unavoidable. Unless a new arms race begins, the number of tanks in service will slowly decline year by year. Meanwhile, the number of "smart weapons" grows rapidly. The tank won't completely disappear soon, but never again will it be the key weapon for ground warfare.
For several decades, the main battle tank has been declared obsolete. Like the battleship, another weapon that depended on big guns and thick armor, the tank was seen as inevitably done in by faster, cheaper and more numerous weapons. The first modern battleship was launched in 1906, but aircraft and submarines made the battleship obsolete, and none were built after 1945. The tank has lasted longer than that. First appearing in combat during World War I, the tank became a decisive weapon during World War II and continued to dominate battlefields to the present. That's over 80 years, twice as long as the battleship. But the tank, like the battleship, became too expensive and too vulnerable to cheaper weapons.