The US will face more competition at the top of a multi-polar global system
US economic, military and political dominance is likely to decline over the next two decades, according to a new US intelligence report on global trends.
The National Intelligence Council (NIC) predicts China, India and Russia will increasingly challenge US influence.
It also says the dollar may no longer be the world's major currency, and food and water shortages will fuel conflict.
However, the report concedes that these outcomes are not inevitable and will depend on the actions of world leaders.
It will make sombre reading for President-elect Barack Obama, the BBC's Jonathan Beale in Washington says, as it paints a bleak picture of the future of US influence and power.
"The next 20 years of transition to a new system are fraught with risks," says Global Trends 2025, the latest of the reports that the NIC prepares every four years in time for the next presidential term.
Washington will retain its considerable military advantages, but scientific and technological advances; the use of "irregular warfare tactics"; the proliferation of long-range precision weapons; and the growing use of cyber warfare "increasingly will constrict US freedom of action", it adds.
Nevertheless, the report concludes: "The US will remain the single most important actor but will be less dominant."
Nuclear weapons use
The NIC's 2004 study painted a rosier picture of America's global position, with US dominance expected to continue.
But the latest Global Trends report says that rising economies such as China, India, Russia and Brazil will offer the US more competition at the top of a multi-polar international system.
The EU is meanwhile predicted to become a "hobbled giant", unable to turn its economic power into diplomatic or military muscle.
A world with more power centres will be less stable than one with one or two superpowers, it says, offering more potential for conflict.
Global warming, along with rising populations and economic growth will put additional strains on natural resources, it warns, fuelling conflict around the globe as countries compete for them.
"Strategic rivalries are most likely to revolve around trade, investments and technological innovation and acquisition, but we cannot rule out a 19th Century-like scenario of arms races, territorial expansion and military rivalries," the report says.
"Types of conflict we have not seen for a while - such as over resources - could re-emerge."
There will be greater potential for conflict in the future, the NIC says
Such conflicts and resource shortages could lead to the collapse of governments in Africa and South Asia, and the rise of organised crime in Eastern and Central Europe, it adds.
And the use of nuclear weapons will grow increasingly likely, the report says, as "rogue states" and militant groups gain greater access to them.
But al-Qaeda could decay "sooner than people think", it adds, citing the group's growing unpopularity in the Muslim world.
"The prospect that al-Qaeda will be among the small number of groups able to transcend the generational timeline is not high, given its harsh ideology, unachievable strategic objectives and inability to become a mass movement," it says.
The NIC does, however, give some scope for leaders to take action to prevent the emergence of new conflicts.
"It is not beyond the mind of human beings, or political systems, [or] in some cases [the] working of market mechanisms to address and alleviate if not solve these problems," said Thomas Fingar, chairman of the NIC.
And, our correspondent adds, it is worth noting that US intelligence has been wrong before.