July 23, 2024:
Since 1949, NATO has been preparing to defend Western Europe from a Russian attack. Until 1989 Russia had massed several hundred thousand troops in East Germany along with several thousand tanks, most of them T-72s. There were thousands more tanks waiting in Ukraine, then part of the Soviet Union. Starting in 1989, when the wall dividing Russian controlled east Berlin from the NATO controlled west Berlin came down, the situation began to change.
Back then Russia was called the Soviet Union because it had more territory and twice as many people as the current Russian Federation. In 1991 the Soviet Union collapsed into 14 independent nations. Two of the largest were the Russian Federation and Ukraine. The current Russian leader Vladimir Putin always wanted to put the Soviet Union back together and he began to do that in early 2022 when he invaded Ukraine. Ukraine was seeking to join NATO and their application was being processed. To be a NATO member Ukraine had to acquire Western tanks and warplanes because NATO is about all members using similar weapons, not Russian ones. The Ukrainians were in the process of converting when Russia attacked. That was because Russia wanted Ukraine to be part of the new Russian Empire, not the NATO alliance that defended members from Russian aggression.
The Russian attack did not go well, with their initial attack force losing most of their tanks and half a million soldiers dead, wounded, missing or taken prisoner. This was a startling revelation to NATO and a major disappointment to Russia. NATO amassed substantial forces to defeat a Russian attack and that attack eventually came, in early 2022, against NATO applicant Ukraine. This clarified the long unanswered question of what would have happened if Russia had attacked NATO forces during the 1949-91 Cold War. The Russian attack against Ukraine was not as massive as the one the Soviet Union forces in Eastern Europe were prepared to make against NATO forces in West Germany and beyond.
The Ukrainians halted the Russian attack and inflicted heavy casualties on the Russians while doing so. After a year of fighting the Russians had lost most of their modern tanks along with nearly half a million troops killed, wounded or missing. A growing number of Russian soldiers preferred desertion or surrendering to Ukrainian forces to dying in Ukraine. Over a million military age Russian men left the country legally or otherwise to escape military service and the possibility of death or disabling wounds in Ukraine.
Russian tank losses were so heavy that Russia is currently using Cold War era T-64 tanks taken out of storage, refurbished and sent to fight and get destroyed in Ukraine. Russia has lost most of its modern weapons and Ukrainian soldiers are finding dead Russian soldiers armed with World War 1 era Mosin-Nagant rifles. Some 39 million of these rifles were produced between the 1890s and 1973 and Russia had a lot of them in storage for an emergency. That emergency was supposed to be someone else invading Russia, not Russia invading Ukraine, a former part of Russia that does not want to become part of Russia again.
For both NATO and Russia this answers the question of what would have happened if Russia attacked NATO forces during the Cold War. Since Ukraine was not yet a NATO member, NATO could not send troops to assist Ukraine but NATO has sent nearly $200 billion in weapons and equipment to Ukraine. Some NATO members are now suggesting that NATO soldiers be sent to Ukraine, as advisors and trainers for Ukrainian forces. Currently some NATO members send some of their troops to neighboring Poland, a NATO member, to train Ukrainians on how to use and maintain all the weapons and equipment NATO has sent to Ukraine. Most NATO members just train Ukrainians in their home countries. NATO aid played a major role in stopping the Russian invasion and pushing the Russians back.