Since then America has introduced sanctions that target Iran's central bank, the country's main conduit for oil transactions, by penalising any foreign financial institutions doing business with it.

ECONOMIST: Tougher sanctions: From half-hearted to harsh | The

Cyprus had become the main conduit for Russians doing business overseas over the past two decades because of its lower corporate-tax rate and the stronger legal protections offered by a European Union country.

WSJ: Russia Denounces Proposed Cyprus Bank Tax

Humans are the main conduit for invasive species.

NPR: Common Intruders Threaten Galapagos Species

Umm Qasr, Iraq's main port and a vital conduit for humanitarian aid, was secured after several days of guerrilla attacks by Iraqi forces .

ECONOMIST: One week on