Washington (CNN) President Donald Trump on Monday vowed the US will "fight to win" in Afghanistan, extending the 16-year campaign there with a promise to beef up the American military presence while ratcheting up pressure on other countries in the region to help turn the tide.

In a prime-time address before a crowd of US troops, Trump sought to convince the country that he was applying a different strategy to the enduring Afghan conflict. But he offered few details, sticking to broad outlines -- beating back the Taliban, annihilating terrorists and cracking down on Pakistan's harboring of militants -- that shed little daylight between the current and future US approaches to the 16-year war.

What was abundantly clear was that Trump, heeding the advice of the current and former generals by his side, had settled on a strategy that cut directly against his instincts for reducing foreign US military interventions.

"My original instinct was to pull out -- and, historically, I like following my instincts," Trump said. "But all my life I've heard that decisions are much different when you sit behind the desk in the Oval Office. In other words, when you're President of the United States."

A withdrawal, Trump said, would dishonor the US troops who died in Afghanistan and could create a vacuum that would allow terrorist networks to expand, as they did after the full withdrawal of US troops in Iraq.

Still, while Trump signaled the US would increase troop levels in Afghanistan, he offered no indication of how many thousands more US soldiers would be deployed, nor would he discuss troop levels or further plans for military activities, echoing a promise he made on the campaign trail.

"I will not say when we are going to attack, but attack we will," Trump said.

Senior administration officials said the President had agreed to increase troop levels, but noted that Trump delegated the authority to manage troop levels to Secretary of Defense James Mattis in June.

As he prepared to lean on US men and women in uniform for the next phase of the war in Afghanistan, Trump also drew on those soldiers as an example of unity for Americans to follow at a time when racial divisions and bigotry have been magnified.

It was the President's latest attempt to offer an unequivocally unifying message to the country in the wake of his botched response to the incidents in Charlottesville sparked by a white supremacist rally.

"By following the heroic example of those who fought to preserve our republic, we can find the inspiration our country needs to unify, to heal and to remain one nation under God," Trump said, without specifically mentioning the violence in the Virginia city.

"When one part of America hurts, we all hurt. And when one citizen suffers an injustice, we all suffer together. Loyalty to our nation demands loyalty to one another. Love for America requires love for all of its people."

'We will keep our eyes wide open'

Trump became the third US president to put his imprint on what has become the longest-running war in American history, despite fiercely arguing during his presidential campaign that the US should focus more of its attention -- and resources -- on problems at home.

Trump, who in 2013 said the US should fully withdraw from Afghanistan, acknowledged that the weight of the office changes how presidents view certain issues, though his aides insisted Trump's decision was consistent with his campaign rhetoric.

The refined US strategy in Afghanistan and the broader South Asia region will focus on "obliterating ISIS," destroying al-Qaeda in Afghanistan and preventing the Taliban from taking over the country.

To achieve these goals, Trump said he would expand authority for the US to target criminal and terrorist networks in Afghanistan.

Trump also said the US would continue to work to strengthen Afghan security forces, noting that "the stronger the Afghan security forces become, the less we will have to do."

Still, Trump warned that he was not offering a blank check of US support to Afghanistan, insisting that the country will have to continue to show a serious commitment and strides toward addressing persistent issues like corruption.

"Our patience is not unlimited. We will keep our eyes wide open," Trump declared.

JUST WATCHED Paul Ryan pleased with Trump's new strategy Replay More Videos ... MUST WATCH Paul Ryan pleased with Trump's new strategy 01:14

Rapid withdrawal impossible

Trump said a rapid withdrawal from Afghanistan is not feasible, pointing to the lessons the US learned from Iraq, where a vacuum allowed ISIS to grow in the wake of the American withdrawal from that country.

"The consequences of a rapid exit are both predictable and unacceptable," Trump said. "We cannot repeat in Afghanistan the mistake we made Iraq."

Trump drew on his characteristically blunt language as he talked about the terrorists the US is confronting in Afghanistan and around the world and vowed the US will "defeat them handily."

"They are nothing but thugs and criminals and predators and, that's right, losers," Trump said. "We will defeat them and defeat them handily."

The address at Joint Base Myer-Henderson Hall, a US military base adjacent to Arlington National Cemetery, is the most significant national security speech of Trump's presidency to date and reflects the outcome of months of internal administration deliberations to decide the scope of the ongoing military, financial and diplomatic commitment to the longest-running war in US history.

The President reached a decision on the future of the US strategy after a final round of deliberations with his national security team at Camp David on Friday.

Trump's decision comes as Taliban militants have been resurgent in recent months, posting a series of recent gains against Afghan government forces, which are backed by a US-led coalition of NATO allies. ISIS, through a regional affiliate known as ISIS-K, has also established a foothold in Afghanistan in recent years, carrying out a series of deadly terrorist attacks and coordinating assaults with the Taliban.

About 8,400 US troops are currently deployed to Afghanistan. The majority of them -- about 6,900 -- are assigned to the NATO mission to train and advise Afghan security forces alongside approximately 6,000 troops from other NATO countries. The remainder of US forces in Afghanistan carry out counterterrorism missions in the country.

The US officially ended its combat mission in Afghanistan in December 2014 and shifted its mission to focus on counterterrorism operations and training Afghan forces. But President Barack Obama never managed to achieve the complete withdrawal of US forces that he had sought during his time in office.

JUST WATCHED Trump acknowledges flip-flop on Afghanistan Replay More Videos ... MUST WATCH Trump acknowledges flip-flop on Afghanistan 00:45

Warning to Pakistan

The Trump administration has been looking beyond troop numbers, mulling a readjustment of US objectives -- evaluating everything from its support for a centralized Afghan government to its metrics for success in fighting the Taliban and ISIS-K.

On Monday, Trump vowed to change the US approach to dealing with Pakistan, promising to crack down on Pakistan's harboring of terrorist and militant groups.

Trump said that Pakistan has "much to gain" from partnering with the US, but also warned "it has much to lose by continuing to harbor criminals and terrorists."

"The Pakistani people have suffered greatly from terrorism and extremism," Trump said. "Pakistan has also sheltered those same organizations that try every single day to kill our people."

"They are housing the very terrorists we are fighting," Trump said, noting that the US gives Pakistan billions of dollars. "That will have to change and that will change immediately. No partnership can survive a country's harboring of terrorists."

Trump also said the US would pressure India to increase its support for Afghan economic development.

Impact of Bannon-McMaster fight

The months-long debate that preceded Trump's decision on the war's fate frequently burst into public view, pitting two top White House advisers against each other: national security adviser H.R. McMaster and Steve Bannon, the President's chief strategist who was pushed out on Friday, shortly before Trump huddled with his national security team at Camp David.

While McMaster has pushed more hawkish proposals, Bannon has led the internal pushback against those options, arguing that the US should not increase its military and financial commitments after 16 years of war in Afghanistan.

Bannon's arguments in internal deliberations often echoed Trump's rhetoric during the campaign , when he argued against US military interventionist policies and argued the US should instead focus its resources on domestic projects.

It was unclear how Bannon's ouster affected the final round of deliberations.

But as Trump mulled a final decision on Friday, he relied on the counsel of several current and former military officers.

Beyond McMaster and Joint Chiefs of Staff Chairman Gen. Joseph Dunford, Trump also relied on a pair of retired Marine Corps four-star generals: Mattis along with his newly installed chief of staff John Kelly.

Kelly's son, 1st Lt. Robert Kelly, a Marine, was killed in Afghanistan in 2010, making Kelly the highest-ranking military officer to suffer the loss of a child in combat.

Several of the President's advisers on the Afghanistan war have children currently enlisted in the US military, including Kelly and Vice President Mike Pence.

Mattis told reporters on Sunday that Trump reconvened his national security team several times before arriving at a decision on Afghanistan because he "kept asking questions on all of them, and wanting more and more depth on it."

"It caused us to integrate the answers more. In other words, the more pointed he became about what he would look at with that option versus this one, meant we could better define what are the relationships with allies or what are the level of effort needed and what's the cost, the financial cost, and so we just kept sharpening those," Mattis said.