Wrong word.. insurgents is what they are..
Insurgents planning insurrection..
Invasion is what armys do..
I never thought about this in the way you did. You are absolutely right. Just as the insurgents are coming into Iraq from Syria, so are the La Raza types coming in from Mexico. Their aim is to destabilize the economy, split the country racially and eventually take over the area they call Aztlan. If the administration and congress doesn't do something soon there will open fighting and lawlessness as there was in LA after the Rodney King incident.
Not necessarily.
The Western Roman Empire was invaded by a horde of Germans of various tribal affiliations in December, 405 A.D. The irruption was by organized bands consisting of tribal and clan groups, including entire families.
Egypt was invaded by the Sea Peoples in the reigns of Merneptah and Ramesses III, during the XVIIIth and XIXth Dynasties. The latter invasion was accomplished by large tribal groups moving with their entire households: "Land united, our plan will succeed," is what they told one another, according to the Egyptian chronicles. Sound familiar?
The same thing was true of the Aryan invasion of the Dravidian Indus Valley civilization that sacked Harappa and Mohenjo-Daro. Likewise of the Anatolian invasion that sacked Troy II and buried the "treasure of Priam" a thousand years before Priam and Hector defended that same city against the well-greaved Greeks.
Nice stab at taking control of a definition, but usage and history are against you.
You need to look up the word invasion in a dozen dictinoaries, as I have done. An invasion does NOT require an army bearing arms. Locusts can invade, SQUATTERS can invade, diseases can invade.
Invasion: \In*va"sion\, n. [L. invasio: cf. F. invasion. See Invade.] [1913 Webster]
1. The act of invading; the act of encroaching upon the rights or possessions of another; encroachment; trespass.
2. A warlike or hostile entrance into the possessions or domains of another; the incursion of an army for conquest or plunder. [1913 Webster]
3. The incoming or first attack of anything hurtful or pernicious; as, the invasion of a disease.
(Note the order of primary and secondary definitions in Websters)
Your limited definition is very short sighted. Look at it this way: by your definition, 500 armed men crossing the border (Pancho Villa, 1916) constitutes an invasion, but ten million unarmed (for the time being!) men does not.
Which poses the greater long-term threat, especially if the ten million invading men pick up arms later, and refuse to obey the law, go home, or swear loyalty to the invaded country? If their goal is to establish "foreign beachheads" in enclaves? Which consider those enclaves to be territory of their own country, prior to controlling the entire region, in this case, the Southwest?