This danger has been alluded to but not emphasized nearly enough how likely a confrontation between the US and Iran (and ultimately the entire region)is...and will remain as long as US forces are deployed in Iraq.
Today you see the beginnings of a dynamic that, left on it's own, will be the first in a series of escalating confrontations between Iranians and Coalition troops which is very likely to lead to our being drawn into a larger conflict...one which will make the current conflict seem like a walk in the park.
Iran captured 15 British sailors in Iraqi waters today un-apologetically using overwhelming force when it's obvious that was likely to strain an already tense situation between them and the Coalition forces especially with the Iranian nuclear issues in the Security Council right now.
This is not merely a civil war, but a regional sectarian conflict that could easily draw the surrounding sects into supporting or attacking factions in Iraq (Sunni, Shia or Kurd) if they feel the US is taking sides.
It will be the un-foreseen confrontation that could draw us into a war with Iran and ultimately a regional conflict which will last for decades.
The spill-over effect is predictable and almost unavoidable unless we get the hell out of there before some Zarqawi type character figures out how to spark this confrontation...which, mark my words, if we are there in a year will have already happened.