In May, Enbridge, a Canadian company, reversed the flow of a big North American oil pipeline, sending a glut of oil from America's northern plains southward to coastal refineries.

ECONOMIST: Petrol prices

Most financial deals these days between the Middle East and the United States involve the purchase of American assets, but on Wednesday, Dubai reversed the flow by cashing out of a New York skyscraper.

FORBES: Magazine Article

Since October, that concern has become acute as the inward flow has reversed, with hot money now leaving China.

FORBES: China Says Yuan Will Be Fully Convertible Soon

But as Iraq has grown less hospitable to al-Qaeda-style jihadists, the human flow has reversed, with many heading back to Lebanon.

ECONOMIST: Syria and Lebanon

The flow briefly reversed in the 1930s, when economic depression and raids by immigration officials pushed perhaps 400, 000 people many of them American citizens south of the border.

ECONOMIST: America's population

"The net migration flow from Mexico to the United States has stopped and may have reversed, " says the report, which is based on an analysis of U.S. and Mexican government data by the nonpartisan Pew Hispanic Center.

WSJ: Mexican Immigration Wave Winds Down