Every continent bar Antarctica now has its own frontier-lowering trade pact.

ECONOMIST: Good fences

New Delhi and Beijing continue to contest large parts of their shared 4, 000-kilometer Himalayan frontier, despite warming trade relations between the nations.

WSJ: India's Missile Launch Puts China in Range

He says frontier markets now, unusually, trade for lower multiples to earnings than their emerging-market peers.

WSJ: Upside: How to Play Investing's Wild Frontier

To take up the slack, many Ukrainians who live near their western frontier have become dependent on border trade.

ECONOMIST: Worried in western Ukraine

Last week, the Thai premier moved to reverse the spiral by signing accords to promote trade and better resolve frontier disputes.

CNN: MYANMAR

Brazil's media worry that the drug trade and refugees may be pushed across the frontier.

ECONOMIST: Colombia and its neighbours

The next frontier in our relationship will be building stronger ties of trade and commerce that match the security cooperation we have achieved.

WHITEHOUSE: The White House

The implications of such an outcome could be far-reaching for the integrity of our southern frontier, illegal immigration, drug-trafficking, terrorism, trade and the radical "reconquista" movement (which is intent on "taking back" at least parts of the United States for Mexico).

CENTERFORSECURITYPOLICY: Who's losing Latin America?

Scottish financiers were also instrumental in financing America's frontier, bankrolling the U.S.' cotton and sugar trade, banks, cattle ranches and railroads.

FORBES: Golden age redux

The final frontier is rapidly approaching: direct trading of overseas-listed stocks through discount brokers such as E-Trade and Schwab.

FORBES: Creating A Borderless Portfolio