The US is overwhelmed by Russia’s military capabilities so they began mobilizing forces to catch up. The US units commander in Europe, General Ben Hodges, acknowledged the recent steps taken by Russia in the Crimea, Donbass and Syria to be completely unexpected.
No evidence given for the claims of an arms race. General Ben Hodges has expressed his concerns that the Russian military exercise Zapad 2017 was surprisingly large and fast. The United States and Russia are informing each other about what exercises will take place and how many soldiers will participate in them, but Russia is lacking in transparency on these issues and, as a rule, exercises are more extensive than the Russians claim. The US is worried because, as part of the Zapad 2017, the Russians practiced tactics that "were later used in Russia's annexation of Crimea in 2014, its support for separatists in eastern Ukraine and its intervention in Syria." For this reason, they mobilize (not increase) military forces, especially in the Baltics, which lies on the border with Russia.