context: After a NASA deep-space probe crash lands in Mexico, alien life-forms spread throughout the U.S.Mexico border region leading to the quarantine of half of Mexico. The U.S. and Mexican militaries battle to contain the creatures with air-strikes and defoliation, while a wall stretching along the American border keeps the United States protected. The film begins with night vision footage of a US Army patrol driving through a town in the middle of the night. An explosion flips one of the vehicles, and fragmented flashes of gunfire show US soldiers firing at an enormous tentacled creature that ambushed the patrol. In the background a radio transmission from one of the soldiers obtains approval for a dangerously close airstrike. Meanwhile a civilian screams for help and attempts to drag a woman off the road and away from the creature. The soldiers withdraw as the man is left behind, lifting the woman and trying to carry her away. Moments later an air-to-ground missile homes on the creature's head.The main plot thread begins a few days prior to the ambush. Andrew, a young American photojournalist in Mexico is hired by his wealthy employer to get the latter's daughter, Samantha, back to the United States. The pair's introduction does not go well: Andrew has no interest in being a chaperone, is haunted that he will miss the birthday of his estranged six year old son, and is troubled by a job that forces him to photograph only the destruction caused by the alien creatures rather than the fact that people are living alongside them. Samantha, meanwhile, is going through a crisis regarding her own position in life, her relationship with her father, and her impending marriage.While travelling to the coast to get a boat to the United States, the pair are temporarily curtailed by the destruction of the railroad and find out that the aliens' migration season is beginning early. If they do not leave the country within a few days, sea and air travel will be blocked and they will have to wait six months before another window is available.Arriving at the port, Andrew is forced to spend $5000 to buy Samantha a ferry ticket to return to America. That night they drink together and begin to open up to each other, but when it becomes obvious Samantha is not interested in him romantically, Andrew gets drunk and sleeps with a random girl from the area. When Samantha wakes up and goes to Andrew's room to say her goodbyes, she finds him with the girl and leaves. She is unable to get on the ferry, however, as Andrew has her passport - and he finds that both his and her passports have been stolen. With the ferry gone, the only possibility of reaching America within a reasonable time is go through the "Infected Zone." In order to bribe their way through the checkpoint, Samantha has to give over her expensive engagement ring.Their journey takes them across Central America by boat (where they see the destruction wrought by the aliens, but also an increasing return of nature in these untouched areas) and by convoy with armed guards (here they are shown the creatures are terraforming the earth, and are attacked by one of the monsters). Over the course of these encounters the pairs relationship grows from a friendship to a romance. Eventually they arrive at the large border wall separating the Infected Zone from the United States. As they cross the checkpoint there, Andrew and Samantha realize the entire Texas region has been evacuated and the aliens have advanced far into United States territory. After walking along an evacuation route, the two stumble across an abandoned gas station. Andrew calls the police, who say the pair are lucky to be alive and that an Army rescue patrol is in the area.Andrew and Samantha both phone their respective families; Andrew his son and Samantha her father, and reconcile with them. Suddenly, an alien appears to attack the gas station, but it turns out there are in fact two aliens who are communicating with each other in a non-threatening way. As the main characters watch, Samantha whispers tearfully, "I don't want to go home." Andrew and Samantha share a lingering kiss, broken only when the army arrives and bundles them into their HMMWVs. As the screen fades to black the story loops to the opening scene, with the army patrol seen driving along the abandoned road at night and the creature attack on the group.
question: What happens when the military appears?
answer: They are ambushed by an alien