Only cursory attention is being paid to the current situation in Ukraine / Russia.
Those who hold historical references are quick to note a combination of factors will generally lead to invasion:
1.) Talk of protecting ethnic Russians.  2.) Dismissal of international opinion.  3.) Weak to non-existent risk of military intervention.  4.) High internal favorability.   All of these factors are currently present.
So will Russia Invade ?
[polldaddy poll=8231380]
DONETSK, Ukraine (AP) — The steadily advancing Ukrainian army is setting its sights on the largest rebel-held city in eastern Ukraine, while Western officials on Wednesday warned that a Russian military buildup on Ukraine’s border could herald a major incursion to protect the separatists.

President Vladimir Putin has resisted mounting pressure from Russian nationalists to send the army in to back the mutiny in eastern Ukraine. Even though the U.S. and NATO would be unlikely to respond militarily, the West would be certain to impose major sanctions that would put the shaky Russian economy on its knees — and could quickly erode Putin’s power.
Russia already is showing signs of economic dismay from sanctions imposed earlier this year, and U.S. President Barack Obama on Wednesday said U.S. sanctions against Russia are straining the country’s economy.
But Putin on Wednesday showed Moscow aims to fight back, calling on government agencies to develop a list of agricultural imports from sanctions-imposing countries that could be banned for up to a year.
The state news agency RIA Novosti later quoted an official from Russia’s plant and veterinary oversight service as saying all U.S. agricultural products would fall under the ban.  (read more)