SEOUL (Reuters) - By the time Donald Trump departed Seoul on Wednesday, the sometimes bellicose American president seemed to have mollified South Koreans who had been bracing for more confrontational rhetoric over North Korea, trade, and defense spending. Throughout his 24-hour swing through South Korea, Trump, who in a September speech at the United Nations had threatened to  totally destroy  North Korea and had dismissed dialogue with Pyongyang as a  waste of time , took a more restrained tone. In his first trip to South Korea as president, Trump also significantly toned down his criticism of what he once called a  horrible  free trade deal with South Korea. He says now he will  find a fair and reciprocal  deal after earlier threatening to terminate the pact. The apparent newfound bond between Trump and liberal South Korean President Moon Jae-in, and the U.S. President s willingness to  make a deal  with North Korea - albeit on his terms - could begin to assuage fears of a catastrophic war with nuclear-armed North Korea.  Trump s willingness to talk about revising the bilateral trade agreement, rather than scrapping it entirely, could also reassure markets worried about the fallout on major exporters such as Samsung, Hyundai and LG Electronics.  Trump s speech to South Korea s National Assembly on Wednesday, interrupted by applause about 20 times with a standing ovation at the end, praised a  free and flourishing  South, in contrast to  the horror of life in North Korea.  On South Korea s largest internet portal, Naver.com, some of Moon s supporters welcomed the address. They said Trump displayed a greater knowledge of the two Koreas than his previous statements had indicated.  Far from the  madman  the media portrays, Trump came across as perfectly normal, smart, and well-mannered,  read one of the more than 1,200 posts on Naver.com. Another wrote:  Wow, best speech ever. I feel so safe to have such a great U.S. president who is so determined to resolve North Korean issues.  Naver.com blocks out the usernames on comments to keep them anonymous.  South Koreans were feeling a little less safe earlier this week when the Pentagon, in a letter to U.S. lawmakers, gave a blunt assessment of what war on the Korea peninsula would look like. A ground invasion would be the only way to locate and secure all North Korea s nuclear weapons with complete certainty, and Pyongyang could use biological and chemical weapons in any conflict, it said. Seoul, the densely populated capital with some 25 million residents, lies an hour s drive from the border.  The U.S. military presence in South Korea has long been seen as a bulwark against the North and its nuclear threat. The United States decisively intervened in the 1950-53 Korean War, which has left the two Korea s technically still at war, since it ended in a truce, not a peace treaty.  While the sprawling U.S. military bases housing some 28,500  troops have not been without controversy  - some critics contend they undermine the country s sovereignty - the U.S. security umbrella is also deeply embedded in the national psyche. Underscoring the importance Seoul attaches to the alliance at a time of increased tensions with Pyongyang, South Korean officials rolled out a reception fit for the first state visit by an American president in 25 years, according to the presidential Blue House. Moon, who took office in May, had campaigned for more dialogue with North Korea. He appeared to be the target of criticism from Trump, who said after North Korea s nuclear test in September:  South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!     But Moon led a charm offensive, proclaiming a  special bond forged between President Trump and myself  after a lengthy meeting at the presidential Blue House. He personally joined Trump during a tour of a U.S. base, as well as during an ultimately aborted visit to the demilitarized zone on the border with North Korea.  I wouldn t say we didn t have any concerns,  a South Korean government official said.  But the fact that he received a standing ovation (for his speech) could mean that he dispelled such concerns, delivered the message we wanted him to deliver, and wrapped up his trip successfully,  said the official who  asked for anonymity, citing the sensitivity of the matter. In his speech to the National Assembly, where several lawmakers brandished signs reading  No war, we want peace ,  Trump paid homage to the 67-year-old alliance that  divides the oppressed and the free . He noted that in  less than one lifetime, South Korea climbed from total devastation to among the wealthiest nations on earth . Trump also reassured South Koreans the Korean War would not be repeated.  We will not allow American cities to be threatened with destruction. We will not be intimidated. And we will not let the worst atrocities in history be repeated here, on this ground we fought and died so hard to secure,  he said. And while Trump painted a dystopian picture of life in North Korea, he refrained from any threats of pre-emptive action against the North. On Tuesday, Trump said it would in the North s interest to  come to the table and to make a deal . It all seemed reassuring to an anxious South Korean public.   I think people might have felt they got to see the real Trump after he visited South Korea,  said Kim Jun-seok, a political science professor at Dongguk University.  And we heard many things that were positive about South Korea. It was all enough for people to think,  Is this the Trump we know?  