The final episode of 'Animaniacs' aired on November 14th, 1998 and was then followed by a direct-to-video movie.
Since then, it's been re-run on television and is frequently a source of nostalgia for adults of a certain vintage. Therefore, it probably speaks to the age profile of the writers on 'Late Show with Stephen Colbert' that they happily busted out a well-known segment from the cartoon for their cold open.
Anyone who watched 'Animaniacs' will remember 'Yakko's World' and 'Wakko's America', where Yakko and Wakko sang the nations of the world and states of America. Chances are if you watched 'Animaniacs' in the '90s, you learned more from that segment than anything you learned in school.
Anyway, 'Late Show with Stephen Colbert' used the 'Wakko's America' segment to help teach Donald Trump a lesson on US geography, owing to his most recent racist comments in which he told four Democrat congresswomen to go back to their own countries, as they were women of colour.
Here's the segment in full.