I don't really want to make a new thread so I will talk about it hear. This is from wikipedia about ID4:
The possibility of a sequel had long been discussed,
[78] and Devlin once stated the world's reaction to the
September 11th attacks influenced him to strongly consider making a sequel to the film.
[79][80] Devlin began writing an outline for a script with Emmerich,
[81] but in May 2004, Emmerich said he and Devlin had attempted to "figure out a way how to continue the story", but that this ultimately did not work, and the pair abandoned the idea.
[82]
In October 2009, Emmerich said he once again had plans for a sequel,
[83] and has since considered the idea of making two sequels to form a trilogy.
[84][85]
How would they even get two more movies out of those? We know how to destroy the alien ships.