Have they explained the story? From what I understand Xcom lost the war, but is winning the first game not canon?
XCOM fought off the actual militaristic offence but aliens launched another, much more insidious and sinister campaign.
You see, aliens realized they don't need to overwhelm hu-mans, that they only need to brainwash them and I'm not even talking about mind-fucks.
They sent infiltrators to start campaigns in media, twitters, facebooks and other signs of hu-man cancer. The leftists that were running rampant by then were easily swayed to protect those poor misunderstood oppressed creatures.
Soon, anyone who wasn't an alien-loving scum was labelled homo sapiens sapiens-scum, extrat-phobe, worse than Hitler and else. Rags such as Guardian, Jezebel, Saloon and similar were more than happy to offer what's left of their minds and dignity, launching #xenolivesmatter, #xenoappreciationday and #xenohistoryday on twitter. It didn't take long for the humanity to drop and its knees and start slurping on those delicious multi-headed tentacles and snaketits.
Alas, the XCOM commend wasn't trained in culture warfare.