Humanity had its first official contact with extraterrestrials in the mid 21st century. Apparently, they had been monitoring our television broadcasts for decades, watching our culture and waiting for us to show that we had something worth contributing to the intergalactic community.
What finally got them was a certain beer ad created in the late 20th century. They had been interested in the invention of beer for quite some time, it being apparently unique in the galaxy, but it wasn’t until they saw this commercial that they really felt they had to try it.
Unfortunately, when they got here they landed in St. Louis. Sorely disappointed at the quality of the beverage they found, they destroyed the city and were just about ready to blow up the entire planet as well, until a small group of alien exiles who’d been living in Germany radioed them and told them to give beer a second chance.
The expeditionary force headed over to Berlin, was greatly overjoyed at what they found and proceeded to get completely trashed. Humanity will never forget the events of that infamous night, the so-called Überverrücktefremdebetrunknenberlinernacht.
The next day the aliens met with the UN, bringing premium alcoholic beverages from across the galaxy. Pretty soon all the delegates were wearing lampshades on their heads and the treaty had been signed that made Earth a member of the Galactic Federation. The rest, as they say, is history.
Though I’m pretty sure they just say that because everyone was too drunk to remember what happened.