During the cold war, Zapad 17 was the biggest military training with over 100,000 military personnel in participation. Upon the collapse of the Soviet Union, the ashes of Zapad 17 were buried only to be exhumed in 1999.
Zapad 17 has created a mild but steady suspicion against a backdrop of political tension in the East and West. This tension aggravated when the US Congress slapped Russia with a series of sanctions for alleged interference with the last presidential election. Although Putin reassured Trump that no such interference occurred, there are staggering chains of event that cannot be jettisoned, not even for Trump or Putin. This has strengthen the strain in US/Russian relationship, a difficulty Trump has strived to rectify.
But the question on many minds as Zapad 17 unravel is whether Putin has an hidden agenda. Russia is claiming not to exceed 13,000 personnel in the exercise, but a senior Polish official has observed that Russia ordered 4000 railcars to transport troops to Belarus and that could amount to over 30,000 military personnel. Russia made similar claims 13,000 personnel in its 2013 Zapad only to surprise the world with over 70,000 personnel in training.
The circumstances are different now because of the tension and NATO is taking a cursory notice of the situation. But report from the NATO headquarters in Brussels make it clear that no interference is planned against the Russian exercise. NATO'S biggest event this year, trident javelin 17, will take place in November with an estimated 3000 troops. While this is NATO'S position, it will be irrational on Putin's end to start an annexation/war. A war on a NATO ally is a war on all and that's too much fronts for Russia to conquer. The US Vice President, Mike Pence, also mentioned the possibility of installation of missiles defence system in Estonia. The world is watching and anticipating all of Putin's unpredictable moves. Some can sense an annexation in the Baltic states where this exercise is scheduled to take place but unlike Crimea, this will be devastating. The grounds of exercise are Belarus, Kaliningrad and Russia. The background of exercise revolves round political tension but all hopes are that it does not exceed a military training.