After World War II, the United States of America acted both militarily and diplomatically to prevent Russia from expanding its territory.
Hundred of thousands of United States armed personnel are stationed in Europe and are ready to act under our NATO commitment to defend any member who is attacked.
NATO has long been an irritant to Putin who appears to have expansionary ambitions. It is reasonable to say that without a robust NATO, there may very well have been war in Europe between the end of World War II and today.
It is in the interests of Putin's Russia then to weaken NATO militarily.
President trump has publicly stated that he wants other NATO members to pay more for their protection; that statement has the appearance of a division in NATO and makes it appear weaker.
A second and very active part of the check on Putin's Russia expansion has been the 'soft' power that the United States Department of State has actively projected in Europe. That power has consisted of State Department personnel maintaining contacts with Western European officials and helping to ensure a cohesive set of polices throughout the diverse continent.
Seemingly at the behest of Putin, Tillerson and trump have unilaterally ended that practice. Tillerson fired most of the career diplomats who have worked diligently to keep Putin in check.
The 'soft power' of the United States of America has ceased to exist.
The likelihood of war in Europe has increased substantially.
Putin thinks has has a green light.