Original Macross in a nutshell for people who want to know what the fuck is going on in Frontier:
-1999, an alien ship crashes to earth, people rebuild the ship and use the technology on it to create fighter planes that transform into giant robots.
-10 years later, on the day the ship is going to embark on its maiden voyage, aliens called the Zentradi (who are essentially giant humans, though they can shrink down to human-sized 'miclones' as well) attack earth, the ship (called the SDF Macross) hyperspace folds from Earth to Pluto and accidentally takes the surrounding city with it, which is rebuilt inside the ship.
-Over the course of the next dozen or so episodes, we find out that the Zentradi basically don't do anything other than fight wars, they have no entertainment and contact between sexes is all but forbidden (people are grown in tubes), so exposure to human culture and the emotions it creates in them shocks the Zentradi (particularly exposure to music or love between men and women.)
-Eventually the Zentradi decide they like culture too much to wipe the humans out so they sign a peace treaty with them- well, the relatively small fleet that's been attacking them, anyway, upon hearing this the other 99% of the Zentradi forces come to Earth and kill every last person on the planet, making the people on the Macross (who manage to fight back the fleet despite being drastically outnumbered by broadcasting a song to them among other hax) the last remaining humans, humanity rebuilds, timeskip to two years later where more shit happens, etc etc.
-Among all this there's a love triangle between a fighter pilot(Hikaru), an aspiring singer(Minmay), and an older military chick(Misa). Misa wins.
That's... about all you need to know and then some, if you want to not be clueless about the backstory of Frontier. The show itself goes over some but not all of this.