President Barack Obama said that U.S. troops stationed in Australia will help ensure the security of vital sea lanes. Darwin, Australia's northernmost city, will become home to joint military training exercises as part of what Obama called a "deliberate and strategic decision" to secure a long-term U.S. role in an area that accounts for half the world’s economy. "This is part of the entire process of strengthening relationships against China," said Robert Dujarric of Temple University, Japan Campus.