The American soldiers are “military advisors”, ostensibly members of Blackwater private army (renamed Academi); a few hundred of them patrol Kiev while others try to suppress the revolt in Donetsk. Officially, they were invited by the new West-installed regime. They are the spearhead of the US invasion attempting to prop up the regime and break down all resistance. They have already bloodied their hands in Donetsk.
Besides, the Pentagon has doubled the number of US fighter jets on a NATO air patrol mission in the Baltics; the US air carrier entered the Black Sea, some US Marines reportedly landed in Lvov “as a part of pre-planned manoeuvres”.
The Russian soldiers ostensibly belong to the Russian Fleet, legally stationed in Crimea. They were in Crimea before the coup, in accordance with the Russian-Ukrainian treaty (like the US 5th fleet in Kuwait), but their presence was probably beefed up. Additional Russian troops were invited in by deposed but legitimately elected President Yanukovych (compare this with the US landing on Haiti in support of the deposed President Aristide ). They help the local pro-Russian militia maintain order, and no one gets killed in the process. In addition, Russia brought its troops on alert and returned a few warships to the Black Sea.
from ICH more here
from ICH more here