Fragility

The planet was crowded, getting short on resources and people were actively changing the ecosystems. Global warming was screwing up coastlines, changing weather patterns and it was time to speak up.
So a group of concerned people formed a group to spread the message, far and wide just how fragile our planet was. Backed by a big liberal groups with money, the started a campaign to educate people, one that included massive broadcasts, both radio and television, to get the message out how little it would take to push things over the edge, how few reserves humans actually had.
Of course, once those broadcasts reached far enough, the message did get received, loud and clear.
Nobody expected just how easy things would come apart after the Aliens got here, nor how easy it would be to knock over human civilization and make slaves of mankind.