Tecate Peak, California, on a cloudy morning, next to US/Mexico border.
No walls out here. The mountains are the "border" wall, 3,000 to 4,000 foot elevation. Before 1996, it had a forest of trees. Over the years several wildfires have made it brush & boulders now.
Millions of people, now in USA today, would tell you that they made the climb over these wilderness ridges... to avoid Border Patrol Agents, and make it north into USA.
Before 1492, only Kumeyaay Culture Indigenous people out here... going back several thousand years, with their tribal descendants still here today, on land called "reservations".
Spain colonized this region for the Vatican to extend the reach of Catholicism. Then this morphed into República de México 1821 - 1846, with Church lands & Native lands taken for Mexican Land Grants.
Then USA gained this terrain by Treaty Of Guadalupe 1848. USA forced the local indigenous tribes to sign worthless treaties that mostly were never ratified. The Treaty Of Santa Ysabel 1852 promised vast terrain, and new infrastructure, signed by Chief Secuan, it was never fulfilled.
DNA studies show that humans walked into Alaska from Siberia during last Ice Age, when world oceans lowered. Humans migrated into the Americas back then, and humans still migrate today. It will never stop.
Nations full of corrupt government, full of criminal elements (gangs & cartels), lacking legal economic chances, and with depressed national currencies, will force their people to migrate. Good people, and the not-so-goods. Anybody willing & able to climb over mountains has a chance.
Will this become "Game Of Thrones" ?
770,000,000 humans live among the nations to south of USA, with people from around the world gaining entry to South American nations.
Primary concern is resistant strains of Tuberculosis will also migrate inside of humans, due to poor health systems in 3rd World nations. TB killed many children across USA in 1800's into 1900's. It is a very stubborn infection.
The people... will migrate.