In March the United States announced that, as of 2017, an American combat brigade would be permanently stationed in East Europe. The troops would serve there for a year then return and be replaced with the personnel from another brigade. In effect the Americans are moving from a policy of “assurance” (to act on the mutual defense clause of the NATO treaty by coming to the aid of NATO members in East Europe under attack by Russia) to a policy of “deterrence” (which is assurance with the addition of U.S. troops already there to face any Russian aggression will guarantee American reinforcements).
The East European nations have long wanted this and all concerned are aware of the fact that the United States provided assurance and deterrence to West Europe, Japan and South Korea during the Cold War.
Americans and West Europeans are also under pressure from East Europe to not repeat what happened in 1939 when West Europe was not willing or able to deal with the German and Russian takeover of Poland, the Baltic States and much else. That sort of history has been known to repeat itself again and again and maybe it can be stopped the next time Russia tries to expand westward.
If this sounds like the Cold War is returning to Europe, it is. There are other signs of this. For example the Americans are reviving the REFORGER exercises. As part of this the U.S. Army plans to store more pre-positioned military equipment in Europe and have brigades move their personnel to Europe for training with that equipment each year. The pre-positioning of equipment continued after the Cold War ended in 1991 but the annual troop movement exercises (REFORGER) to use the pre-positioned equipment stopped. Now it is being resumed with at least one brigade a year being sent to Europe to use the pre-positioned equipment for training exercises aimed at defending East Europe against Russia. Just like the Cold War, except then the Russian armies were already in East Europe before 1991 and it was Western Europe being defended.
This practice of moving troops and equipment as separate entities was a Cold War innovation. To speed the movement of reinforcements from the United States to Europe, in the event that the Soviet Union invading, two divisions had one set of equipment in Europe, and another back in the United States, where the divisions were based. In reality this pre-positioning and troop movement plan also served political demands in the United States that some of the divisions stationed there be brought home. The pre-positioning was a politically acceptable way to withdraw two divisions from Europe. This was done in 1968, but the equipment stayed behind, and was stored and maintained by contractors (German civilians). Starting in 1969 troops from the two withdrawn divisions began flying to Europe each year, firing up the gear, and going out on field exercises. The troops would then return the gear to the storage areas and fly home. These annual exercises lasted until 1988.
The experience gained in all those REFORGER exercises made the army and marines confident that they could apply the concept of pre-positioned equipment elsewhere in the future. This also led to the idea, as applied in Iraq from 2004 to 2011 of having the first units to get there to leave their gear behind (if they were being replaced by the same type units) when the troops returned home. This saved a lot of money in shipping costs, not to mention the additional work the troops had to do preparing everything for sea movement. Same deal in Afghanistan and the REFORGER techniques have become standards.