Equestria and Earth have a portal! Wheeee! Heroes and hero worship abound, but so does tourism, business, and the frontiers of science. During a guest appearance at and American College, Rainbow Dash explains how the water cycle works for Non-Equestrians of higher education.
And gets called out.
And responds the only way she knows how... by being AWESOME.
Which results in a diplomatic nightmare and the president of 'Merca having to throw down the laws of the land.

Which Equestria simply won't accept. It's high time that Twilight Sparkle broke out the RECSMA and brought all of Equestria's not-insignificant historical might to bare.

Silly 'Merca.