This CNN article: Chavez threatens to cut off oil to U.S. discusses a threat by Hugo Chavez to cut off Venezuela's shipments of oil to the U.S. Part of this has been an ongoing story, for example the American-backed coup attempt in Venezuela a couple years ago.
Chavez has been making statements for years about vague threats against him by the U.S. They might sound like the ravings of paranoia, except that there was this weird coup which started to topple him out of power. A coup which was clearly inspired by American interests. And, there is the long history of the U.S. toppling governments in the Western Hemisphere through following the Monroe Doctrine, in which President Monroe declared to the world, "The Western Hemisphere is ours, and you can't have it" and which has justified repeated actions by the U.S. government against western hemisphere governments from at least the Dominican Republic, to Allende's government in Chile, to the invasions of Grenada and Panama.
A part of the game playing between the U.S. and Venezuela is repeated expulsions of diplomats over allegations of spying.
Which just reminds me of: The confessions of an economic hit-man an interview I heard on Democracy Now a few days ago. The interviewee, John Perkins, had written a book exposing, as a former insider to the game, how the U.S. government has quietly created a worldwide economic empire. A part of that game is to make deals with world leaders where people like him would meet newly elected world leaders and offer them a deal. In one hand the economic hit man will offer riches, kickbacks for example from the sale of whatever resources that country has. In the other hand the economic hit man will hold a threat of violence against that leader or his/her family. These leaders know the history and know that legions of previous world leaders have been assassinated or overthrown by these people.