this is "nightline." >> tonight, on the brink? the american troops mobilizing. the stunning scene. a nation vowing revenge and mourning the death of their commander killed by a u.s. drone strike. our martha raddatz with rare on-the-ground access. >> revenge must happen. plus inferno down under. the worst wildfires to hit the continent in modern history. now the u.s. firefighters joining the fight. abc's maggie rulli on the front lines. >> the heat radiating off this flame is so intense right now. >> the race to tame the raging flames. and save as many creatures,

great and small. >> we have lost thousands, thousands of koalas, thousands of so many other species, it's just criminal. >> but first the "nightline 5." >> when you never lower your standards, only your fares, it's a better class of sale. emirates. fly better. emirates. ♪ ♪

♪ ♪ ♪ blow a kiss into the sun ♪ we need someone to lean on ♪ blow a kiss into the sun ♪ all we needed somebody to lean on ♪ ♪ ♪ good evening. thanks for join is us. tonight, american troops on the move as the cry for revenge in

iran grows. a u.s. drone strike killing a revered iranian military commander. what this means for two nations caught in years of simmering tensions now thrust into uncharted territory. these young american servicemen and women are the first wave of military troops arriving in the middle east amid the growing crisis with iran. 3,500 strong joining the already tens of thousands of u.s. troops in the region. tensions flaring after a u.s. drone strike last week killed iran's top military official, general qasem soleimani. in the heart of iran a public outpouring of grief overwhelming the streets of its capital. >> trump made a big mistake. he killed our hero. >> reporter: cries drowned out by angry chants. soleimani, a beloved figure in iran, seen as standing up to the

west. now his death and the way it was carried out a game changer for iran and the united states. >> you don't have any right to kill him. >> reporter: my colleague, martha raddatz, one of the few western journalists allowed in the country. >> this procession so packed you can barely move but the emotion is everywhere. people have a very strong message for america. >> reporter: they're chanting "death to america." inside the funeral service, tears from iran's supreme leader, ayatollah what mainny, weeping. >> few figures were held in higher esteem by the iranian people than mr. soleimani. he was the man who brought back pride. >> reporter: on the ground his image everywhere. more than 1 million united in their cry for revenge. >> revenge must happen, and it

is certain. >> what kind of i venge do you want? >> anything. >> reporter: 24-year-old hussein is a college student. >> what is your message to america? >> i'm saying, we love americans but we hate your president. >> reporter: soleimani, a critic of the united states, taunted president trump in a speech in 2018. let me tell you, mr. trump, the gambler, know that we are near you in places that don't come to your mind. the u.s. moved to kill the revered general, who command the elite revolutionary guard, proving consequential across the region. members of the iranian parliament chanting "death to america." and this weekend an ominous sign, a red flag symbolizing war raised above an iranian mosque.

>> we took action last night to stop a war. we did not take action to start a war. >> reporter: in the face of criticism, president trump insisted the attack was a necessary measure. >> sol mainny was plotting imminent and sinister attacks on american diplomats and american personnel, but we caught him in the act and terminated him. >> reporter: but there are questions about the administration's initial justification for the attack. just how imminent those threats were. this evening the chairman of the joint chiefs of staff telling reporters the intelligence was compelling, adding -- >> did it exactly say who, what, when, where? no. but he was planning, coordinating, synchronizing significant combat operations against u.s. military forces in the region, and it was imminent. >> reporter: but the iranians deny those claims, instead pointing to the general's record of fighting isis.

>> reporter: iranian officials threatening retaliation that would target u.s. military in the region. >> whether they punch back is a big calculus, because they know that if they do they're going to be hit hard with conventional attacks on iranian soil. and those attacks could bring down a very fragile economy. >> reporter: over the weekend president trump warned if there is retaliation, he has 52 iranian targets in his sights. some he says at a very high level and important to iran and the iranian culture. a potential war crime under international law. but secretary of state mike pompeo telling abc that no illegal action would be taken. >> every target that we strike will be a lawful target, and it will be a target designed at the singular mission of protecting and defending america. >> reporter: trump contradicted that notion hours later telling reporters off camera that

iranians are allowed to kill our people, they're allowed to torture and maim our people, and we're not allowed to touch their culture sites? it doesn't work that way. tensions in iran impacting relations with neighboring iraq. the iraqi parliament angered at the killing of soleimani on their soil voting to kick the u.s. out of their country. amidst this crisis, the u.s. and nato pausing operations against isis. it's worth noting the last time there was a power vacuum in iraq, isis filled the void. this latest round of escalations began in 2018 after president trump dismantled the iran nuclear deal, brokered by president obama. >> this was a horrible, one-sided deal. >> reporter: today the iranian government announcing they're suspending commitments to that deal, now abandoning limits on

enriching uranium and stockpiling nuclear fuel. hostilities continue to escalate after a series of iranian provocations over this past summer, including the downing of an american drone. then in late december, an american contractor was killed in a rocket attack in iraq. the u.s. blamed an iranian-backed militia and responded with air strikes that killed at least two dozen people, possibly including civilians. on new year's eve, a huge crowd of protesters stormed the u.s. embassy compound in baghdad, breaching the highly fortified perimeter, a two-day siege sent diplomats into a safe room and forced marines to deploy tear gas. president trump blamed iran for orchestrating those protests. ominously tweeting two days before general soleimani was killed, iran is going to pay a very big price, this is not a warning, it is a threat. america's contentious history with iran goes back decades,

back to 1953, when the u.s. installed the shah in order to protect oil interests. after 25 years, in 1979, mass demonstrations filled the streets and forced the shah into exile. then just months later -- >> the u.s. embassy in tehran has been invaded and occupied by iranian students. >> reporter: holding dozens of american hostages for 444 days. before they were released in 1981. the relationship between the u.s. and iran over the next few decades would remain fractured. fast forward to 2013. president barack obama's administration started taking small but controversial steps to bridge decades of hostilities, including a one-on-one conversation with iran's then newly elected president rouhani. in 2015, the u.s., along with a group of world powers, brokered the deal with iran to end its nuclear program. that momentary thawing of

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[ dramatic music ]ing ] ahhhh! -ahhhh! elliott. you came back! huge swaths of australia are struggling to breathe tonight. days of devastating and deadly wildfires destroying homes and

delicate ecosystems, displacing people and animals across the country. now the rescuers hoping to reverse a stark reality. here's abc's maggie rulli. >> reporter: we drive into an inferno. we're struggling to get north right now, hitting roadblock after roadblock. these flames go all the way up and down this highway. it's not just here, it is for miles and miles. a countryside consumed by flames. the wind and heat and flames are really starting to take off. you can hear everything burning behind you. that smoke the eyes. for weeks this has been the reality for the people of australia. >> oh my god, oh my god. apocalyptic, this is the middle of the day. >> holy [ bleep ]. all of my possessions have been totally incinerated. >> reporter: all around the country, homes destroyed by the hundreds. >> go, go! >> reporter: people evacuating

by the thousands. australia's prone to yearly outbreaks, but changing winds, prolonged drought, and record heat have exacerbated the danger, creating a maelstrom engulfing the country in a ring of fire. >> they are spreading through ranches and even the edges of town at hugely quick rates. >> reporter: destroying more than 15 million acres of land. at least 25 people have lost their lives. >> this is just the beginning of their fire season. so we can anticipate even worse impacts in the next weeks. >> reporter: to put this into context in 2018's massive california fires, nearly 2 million acres of land were left to ash. the ones in the amazon, even bigger. but since september, the fires here in australia have already burned more than three times those events combined. for scale, if you superimpose australia over the united states, the fire would spread from california to pennsylvania. now more than 4,500 firefighters and support personnel are trying

to bring this to an end, including 77 from america, 21 more arriving today. firefighters like volunteer steve price from boise, idaho. >> it's the biggest fire i've ever been on in my life, and i've been doing it 32 years now. >> reporter: in the last week, authorities evacuating residents and tourists as fires intensify. in the face of it, some deciding to stay. >> oh my! >> reporter: 19-year-old india mcdonald, surrounded by the inferno with only a garden hose to beat back the flames. >> i can't breathe! >> reporter: she told australia's news 9 that against insurmountable orders, she and her firefighter father were able to save their house. on friday we met paula and david durant. they decided to stay behind and fight the flames at their ranch. >> we're just hoping that, you know, we can save the house if nothing else. >> reporter: we weren't to check on them after saturday's fires tore through. the road to their house was charred with some parts still burning. what was it like here? >> oh, horrific.

horrific. yesterday was really terrible. really bad. i mean -- the heat, no power. we've got limited phone reception. so we sort of, you know, basically can get a few quick messages out to people. >> oh wow, they're still smoking up there. >> yeah, and all the way through here and all the way up there in the hills. we're just putting it out. the seems to have hopefully gone around us a little bit more. >> reporter: the coastal town of mallacoota, 4,000 residents and tourists were forced to shelter on beaches. others taking refuge in boats. some prepared to jump into the water. the sky dark with smoke as fierce winds pushed flames towards them. the evacuation of so many is nearly impossible because of the clouds of dense smoke. the military having to use boats to deliver supplies while they wait. >> when we were in there, in the thick of it, we thought, this could be it. >> reporter: the flames so

perilous, these firefighters in south wales were forced to shelter inside their truck, leaving through a raging inferno. >> it had got to a point where it was too dangerous to remain in the vehicle. >> reporter: a warning to viewers, many of these images are disturbing. nearly 500 million animals are estimated killed. one facebook user posting this haunting video of a sea of animals lying dead on the side of the road. as fires ravage much of australia's fragile ecosystem, the australia zoo, owned by the late steve irwin's family, posting on instagram they've taken in over 90,000 animal patients. >> it's scary when you think of how many are lost and there's still so much you can learn from them. >> we have lost thousands. thousands of koalas, thousands of so many other species. it's just criminal. this is -- this is the worst event this country's ever seen, without a doubt. horrific. >> reporter: shane flanagan is the director at the koala hospital in new south wales. >> you see he's burned there.

but they've all healed. that was all red, raw. and it's all going nicely now. >> reporter: her hospital is a safe haven for koalas, taking in dozens of animals that have been burned or lost their hab bat, koalas like paul. paul went viral after being saved in november at a nature reserve. he was named after the human who rescued him. >> hi, paul. >> see how he's lost teeth? all the fur's growing back. >> reporter: paul is one of the lun lucky ones. it's not just burns that are dangerous to koalas, their environment is being destroyed. the fires and the hot, dry air also make them more susceptible to diseases that could render female koalas infertile. >> this disease with a lot of these burned animals is going to take ought a lot more burnt koalas that have survived the fires, it will kill them. yeah. and with the drought, there's no moisture out there in the eucalyptus leaves, there's no groundwater, so they're all dying of dehydration, burns, and

disease. >> reporter: despite these dangers she says are created by a changing climate, she's determined to protect the species. >> up until when these fires happened, i'd never have thought that would be a possibility. but we have another few seasons like this the next few summers? heaven help the populations out there. and i say, shame, australia. shame. >> reporter: unfortunately, fires approaching this scale are not just an australian problem. >> i can't even see, let's get the hell out of here. >> reporter: over the past few years wildfires have become a global catastrophe, increasing in frequency, size, and severity, from greece to portugal to the california coast left barren by devastating fires. >> we are spewing pollution and carbon dioxide into the atmosphere. the science is pretty clear, that that has impacted our climate in a way to cause extreme conditions. >> you think it's a warning call for americans? >> yes. we've got to change the way we

live. you know, we've got to stop being such big consumers and change it. the time is happening now. mother earth is getting cranky. >> reporter: cranky, yes. but for those staying behind fighting for their home, it's their only hope. >> we're not going to go anywhere because we've been lucky. that's all we can hope is that, you know, it's not coming back. they just keep saying, be prepared, be prepared. >> reporter: a brief break in the weather offering a little relief and some towns are opening back up, but those monster fires are still raging. with more potential he catastrophic conditions expected later this week, the people here say they're living in constant fear. for "nightline," i'm maggie rulli in new south wales, australia. up next, ringing in far more than a new year. a new chance at life. this is my body of proof. proof i can fight moderate to severe rheumatoid arthritis.

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that is 19-year-old matt driscoll, cheered on by family and friends, especially those on the hospital staff in akron, ohio. that's where matt's been getting chemo for the last 3 1/2 years. his last treatment, a bell ringer of a day. celebrating the start of a future free from leukemia. through tears and hugs, matt says it was the happiest day of his life. and of course we're wishing matt and his family health and happiness in 2020. that's "nightline." you can always catch our full episodes on hulu.