12 Million is a small number? 12 Million is an invasion.
Not only are these numbers relative, but numbers do not correlate with "invasion".
As for the numbers part: 12 million is less than 4% of our population. By your standards, the mass immigration at the turn of the 20th Century was an invasion on a much larger scale.
Invasion: (n.) 1. an act of invading, especially: incursion of an army for conquest or plunder; 2. the incoming or spread of something usually hurtful
So, the onus is now to prove that the sole reasons for their immigration are for either conquest or plunder (taking what is not rightfully theirs), or prove that these immigrants are "usually hurtful", wherein usually would have to include greater than 50% of said immigrants.
Best of luck in your endeavor.