• Main international airport: Hartsfield–Jackson, Atlanta, Georgia (79.1m passengers)
• Merchant fleet, total tonnage: 443 ships (15m dwt)

The transportation network

• Extent of inland waterways navigable by commercial craft: 41,009 km (25,482 miles)
• Extent of national paved road network: 371,913 km (231,096 miles)
• Extent of motorways, freeways or major national highways: 74,807 km (46,483 miles)
• Extent of commercial rail network: 235,071 km (146,066 miles)

Arterial river systems provided the first transportation networks in the US. Today, the US has the world's cheapest, most extensive internal air network and a good system of interstate highways. Railroads, comparatively neglected for years, mainly carry freight, though modern high-speed trains are starting to attract passengers back. Americans have been wedded to the car since Henry Ford began mass production in 1908. By 1919 there were nine million cars in the US. Today the total tops 210 million, including pickups and the ubiquitous "sports utes" (SUVs). Americans make more than half of the world's car journeys. Cheap gasoline underpinned the rise of the car; despite problems of congestion and pollution, and the environmental costs of ever more oil production, its centrality in society is rarely questioned.

Isolated by two great oceans, the US has been able for much of its history to choose the extent of its participation in world affairs. Only reluctantly drawn into the two world wars, after 1945 it swapped isolationism for involvement. The US took its seat on the Security Council of the new UN, founded in San Francisco and now based in New York, and helped to set up NATO. For the US the Cold War was most immediate – and costly – in the Korean and Vietnam wars. The death toll and shock of defeat in Vietnam in the 1970s kept the US out of direct military involvement overseas for over a decade. Instead, it focused on diplomacy and on supporting the opponents of left-wing regimes in developing countries including Nicaragua, Cuba, and Angola.

Since the collapse of the Eastern bloc after 1989 the US has had to redetermine the scope of its foreign responsibilities as the only remaining superpower. Until 2001 policy remained cautious. It had led the intervention in the 1991 Gulf War, but a fiasco in Somalia and a lack of clear objectives in Bosnia & Herzegovina and Haiti showed its uncertainty about a role as world policeman. The September 11, 2001, terrorist attacks provoked the Bush regime into reclaiming the international initiative. Bush is inspired in part by the right-wing doctrine of the "new American century," which advocates making use of unrivaled US power to shape world affairs to the country's benefit.

The first act of this new approach was the declaration of a "war on terrorism," which seeks to build a global, US-led consensus in the fight against nonstate combatants. The "successful" war in Afghanistan in late 2001 raised concerns in the Islamic world that Muslims were being unfairly targeted, while global tensions increased in 2002 when Bush declared Iran, Iraq, and North Korea to be an "axis of evil" states which sponsored terrorists.

Threats against Iraq culminated in the 2003 invasion. Many people, particularly in "old" Europe, saw the war as an attempt to settle old scores and seize the riches of Iraq's vast oil reserves, and were concerned when the US did not allow international relations, and specifically the diplomatic wrangling of the UN, to stand in the way of realizing its foreign policy aims.

As a result, global opinion toward the US has grown increasingly negative, potentially fueling the ranks of anti-US terrorist groups: an opposition backed by a popular grassroots movement in the developed world which identifies US military and economic hegemony, as well as its dominant culture, with the perceived evils of globalization.