Integration by migration?

"In terms of trade and capital flows, the Middle East is one of the least economically integrated regions of the world. The major exception is labor mobility, where intraregional migration flows are extensive. The explanation for this pattern lies in the extreme differences in factor endowments across the region and development policies adopted by both labor-importing and exporting countries. Because the obstacles to trade in goods have been greater than the obstacles to migration, labor mobility and its associated capital flows have been the most important mechanism through which the benefits of the oil windfall have been spread to the poorer states of the region. There is evidence that incomes across the Middle East have become more equal."