Washington (CNN) -- The Kremlin sends troops across the border, and the United States and its allies cry foul.
It's happened before -- Afghanistan in 1979, Georgia in 2008 -- and now Russian President Vladimir Putin has essentially seized military control of the Crimean Peninsula from Ukraine.
The move reflects the still simmering political and social upheaval from the breakup of the Soviet Union more than two decades ago.
What hasn't changed much are the limited options available to President Barack Obama and European powers to respond to the Kremlin's aggression.
The United States and some other countries boycotted the Moscow Olympics in 1980, and Washington helped arm Afghan rebels against Soviet forces, who eventually went back home.
In Georgia, Russia backed secessionist bids in the South Ossetia and Abkhazia regions in sovereignty disputes that remain unresolved. The United States and European Union consider the regions part of Georgia.
Here is a look at possible responses to Putin's latest move in Ukraine:
Military
Unless a sudden escalation causes open warfare between Ukraine and Russia, forget about any kind of U.S. or allied military response.
Secretary of State John Kerry said Sunday the United States was keeping its options open, but he made a point of adding that escalated military involvement would "not serve the world well."
"The last thing anybody wants is a military option in this kind of situation," Kerry said on NBC's "Meet the Press."
Even veteran Sen. John McCain of Arizona, a proponent of exerting U.S. influence abroad, conceded that the fight must involve diplomacy, not the military.
"There is not a military option that could be exercised now," McCain said Monday in remarks at the American Israel Public Affairs Committee's annual conference. "But the most powerful and biggest and strongest nation in the world should have plenty of options."
On Monday, the United States put on hold all military-to-military engagements with Russia, an official announced.
"Although the Department of Defense finds value in the military-to-military relationship with the Russian Federation we have developed over the past few years to increase transparency, build understanding, and reduce the risk of military miscalculation, we have, in light of recent events in Ukraine, put on hold all military-to-military engagements between the United States and Russia. This includes exercises, bilateral meetings, port visits and planning conferences," said Pentagon Press Secretary Rear Adm. John Kirby.
He denied reports speculating on possible ship movements in the region.
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