President Donald Trump has declared a new era of competition is under way with the US set to follow his 2016 campaign doctrine of “America First”.

Unveiling the new national security strategy, Mr Trump criticised previous leaders for failing to look out for the nation’s citizens.

“America is in the game, and America is going to win,” he said.

His strategy focuses on protecting the homeland, including building a wall on the US southern border and taking other steps on immigration. He also called for promoting American prosperity, demonstrating peace through strength and advancing American influence.

He said the US will cooperate with other countries “in a manner that always protects our national interests”.

But he insisted that the US “will stand up for ourselves and our country like we have never stood up before”. He called for competing “with every instrument of our national power”.

He denounced previous presidents for engaging in “nation building abroad while they failed to build up and replenish our nation at home”, pointing to the economy’s strong performance and predicting even better under his policies.

His security strategy envisions nations in constant competition, reverses Obama-era warnings on climate change and affirms that the US will unilaterally defend its sovereignty, even if that means risking existing agreements with other countries that have dominated foreign policy since the Cold War.

Mr Trump’s doctrine holds that nation-states are in perpetual competition and that the US must fight on all fronts to protect and defend its sovereignty from friend and foe alike.

While the administration often says that “America First” does not mean “America Alone,” the national security strategy makes clear that the US will stand up for itself even if that means acting unilaterally or alienating others on issues such as trade, climate change and immigration.

The last such strategy document, prepared by President Barack Obama in 2015, declared climate change an “urgent and growing threat to our national security.” The Trump plan removes that determination following the administration’s threat to pull out of the Paris climate accord.

The strategy sets a goal of being an “energy-dominant nation” and says that the US “recognises the importance of environmental stewardship”.

The document removes Obama's description of climate change as 'an urgent and growing threat' The document removes Obama’s description of climate change as ‘an urgent and growing threat’ (Michel Euler/AP)

Despite the risk of potential isolation presented by Mr Trump’s strategy, its fundamentals are not a surprise. The strategy emphasises that US economic security is national security. And it stresses that the US is interested only in relationships with other countries, including in alliances such as Nato, that are fair and reciprocal.

The strategy also details the threats of “rogue regimes,” like North Korea. It says that China and Russia “challenge American power, influence, and interests, attempting to erode American security and prosperity”.

Despite international challenges, the document cites emerging opportunities to advance American interests in the Middle East.

“Some of our partners are working together to reject radical ideologies and key leaders are calling for a rejection of Islamist extremism and violence,” it says. “Encouraging political stability and sustainable prosperity would contribute to dampening the conditions that fuel sectarian grievances.”