China will be the world’s largest economy by 2030 but the US will still remain “first among equals” in the international system, according to a new US government intelligence assessment of global trends.

The report predicts that Europe, Japan and Russia will continue to experience relative decline, and that Asia will come to dwarf the rest of the world in terms of its economic and military power.

Among other conclusions, the wave of Islamist terrorism is likely to have ended by 2030, the survey predicts, the US will be energy independent and could be a significant exporter of energy, and advances in manufacturing technologies could reduce the need for outsourcing. The study also warns that future conflicts in Asia and the Middle East could involve a “nuclear element”.

“With the rapid rise of other countries, the ‘unipolar moment’ is over, and ‘Pax Americana’ – the era of American ascendancy in international politics that began in 1945 – is fast winding down,” the report states. In terms of economic size, technology and military spending, Asian power will exceed North America and Europe combined by 2030.

However, the US will retain its central role because it will remain the only country able to mobilise coalitions to address global challenges.

“No other power has the ability to replicate the US role under any scenario,” said Christopher Kojm, chairman of the National Intelligence Council.

The report, Global Trends 2030, is published by the NIC and reflects the view of the US government’s 16 intelligence agencies on what the world will look like in two decades’ time. The study is published every four years to assist the long-term strategic planning of each new administration.

The broad conclusion about the demise of Pax Americana strikes a sharp contrast to the rhetoric of the recently ended presidential election campaign, during which both candidates charted a vision of continued American pre-eminence.

However, the NIC is slightly more optimistic about the future American role in the world than in its previous report, compiled four years ago at the peak of the financial crisis, which described an international system that would be “unrecognisable” by 2025 and “fraught with risks” because of the decline in American influence.

While the new study recognises the big shifts in relative power taking place around the world, especially in Asia, it is cautious in its assessment of the likely increase in Chinese power and influence, citing its ageing population, environmental problems, the growth in nationalism, potential for unrest, and regional opposition.

“China is the wildcard. Its actions can be its worst enemy,” said Mathew Burrows, the study’s main author, referring to more aggressive Chinese diplomacy in Asia in recent years. “It has ended up creating a lot more support for a continued US role in the region.”

At the same time, the capacity of the US for forming coalitions of allies and friends and of mobilising networks of individuals and non-state actors will give it an advantage, even as it loses its dominant position in terms of “hard” power. However, the report adds: “A divided US would have a more difficult time shaping a new role.”

The study argues that the US could become a substantial exporter of energy as a result of developments in shale gas. If the US were also able to exploit difficult-to-access oil deposits, this could change the dynamics of the global oil market, leading to a loss of power for Opec and a potential “collapse” in oil prices.

Advances in new technologies, such as robotics and 3D printing, could have a huge impact on manufacturing, the report says, boosting productivity and reducing some of the need for outsourcing of production. However, these trends will continue to depress wages of low and semi-skilled workers in developed economies and will also present many new opportunities for Asian manufacturers.

Mr Burrows said it was likely that the cycle of Islamist terrorism would have “exhausted itself” by 2030 because of a lack of popular support in Muslim countries. However, the spread of new technologies was increasing the potential for individuals with skills in cyber systems to help terrorist groups. Climate change and water shortages meant that food prices were likely to continue rising.

According the intelligence assessment, one of the most important trends over the coming two decades will be the growth of the middle class, which “will become the most important social and economic sector in the vast majority of countries around the world”. This will lead to a surge in “individual empowerment”, including improved education and healthcare and widespread use of communications technologies.

Saudi Arabia has cut oil output to its lowest level for a year as a combination of surging US crude production and weakening economic growth sapped demand.

The sharp fall in Saudi production, details of which were published ahead of a meeting in Vienna of the Opec oil cartel, contrasts with surging US energy output as hydraulic fracturing or “fracking” have unlocked vast quantities of shale oil and gas.

Adam Sieminski, head of the US Energy Information Administration, said increased drilling in the tight shale formations of North Dakota, Montana and Texas “will boost US crude oil production above 7m barrels per day next year for the first time since 1992”.

Meanwhile, figures published on the eve of the Vienna meeting of Opec showed that Saudi Arabia pumped 9.5m barrels a day in November, the lowest level in a year and down from the 30-year high of 10.1m b/d set in June.

The fall in Saudi production reduced overall Opec output to 30.78m b/d in November, the lowest in almost a year.

Opec is likely to keep its official output levels unchanged on Wednesday. A year ago it agreed a 30m-barrel-a-day ceiling, but did not assign production quotas to individual members. That gave Saudi a free hand to moderate output, and is a policy that is likely to continue.

Riyadh’s flexible export policy has been credited with keeping oil prices stable in recent months, despite continuing tensions in the Middle East in the aftermath of the Arab Spring. The kingdom increased production to make up for barrels lost to global markets as a result of sanctions against Iran.

Brent crude futures have fluctuated within a range of about $6 in recent weeks, between $106 and $112 a barrel. Brent was 29 cents higher on Tuesday at $107.62.

Even with the cuts, analysts said Opec may have been overproducing, leading to higher oil inventories in industrialised countries. “If Opec continues oil production at these levels into next year, the oversupply will rise, putting downward pressure on prices,” said Carsten Fritsch of Commerzbank.

So far, geopolitical tensions in the Middle East have meant prices have stayed high. The violence in Syria has combined with renewed unrest in Egypt and worries about Iran’s nuclear programme to maintain oil-market jitters.

At their meeting in Vienna, Opec ministers will also try to agree on a new secretary-general. Candidates from Iran, Iraq and Saudi Arabia are vying for the post, currently occupied by Abdalla El-Badri.

The process has been complicated by deep-seated rivalries between Riyadh and Tehran. With no sign of a compromise candidate emerging, ministers are expected to ask Mr El-Badri to stay in the job for another six months.