Re-conquering would require that they once held it. They never conquered it in the first place if you check your history. However, it IS a foreign invasion force bent upon hostile colonization of a foreign power and undermining its economy, security, and eventually its government.
It doesn't matter what you and I think. The Mexicans think the SW belong to them at once. They think they have a right to it. And now, they are coming like a plague. And our leaders welcome the invasion. They want to grant them automatic citizenship for those invaders who have been here for 5+ years. I am very angry seeing those invaders waving Mexican flags on TV when the American flag cannot be displayed. Isn't this a sign when we are being conquered and occupied already?