system
Given the following post, respond as if you're commenting on Reddit:
human
(Independence Day) How did the governments of Earth rebuild their nations after the alien invasion?

and what did they do with all of those city sized motherships that crashed?
gpt
Rebuilding a city from a big blast is not an insurmountable task - Japan's done it twice. 

Many cities also mounted evacuations that saved a large number of citizens, and while the supply chain was certainly disrupted, the fact that the aliens attacked the cities with (seemingly) non-nuclear attacks means that there is no fallout, and that farms will still operate - so the refugees won't necessarily starve. (The bigger problem is that many cities attacked were port cities - it's easier to ship grain overseas than it is over rails.)

As far as the ships, the military forces would establish a security cordon and start investigations. The United States would have a leg-up, since the ship crashed in the middle of an inhospitable desert right next to an advanced research facility, and the only two living humans who are extremely familiar with the technology - a programmer and a pilot with direct hands-on experience. We can reasonably expect the USAF to have undisputed air superiority for decades to follow.

It remains to be seen whether there are going to be any biological consequences - ships of that size might have had members with the sniffles, and who knows how that's going to react with our biology. We're pretty different from the invaders, so their bacteria and viruses probably won't even notice us and vice versa, but the only people who know for sure are in Area 51.