Starting in the 1950's, after World War II, and then following 9/11 and the rise of terrorism, the building of border walls has surged, as noted by the following graph from the Migration Policy Institute:
Decades ago, the poet Robert Frost wrote 'Mending Wall'. The poem opened with the line "Something there is that doesn’t love a wall" and also contained these words: "Good fences make good neighbors". Many falsely believed that Frost was arguing for the building of walls. However, 'Mending Walls' was actually an anti-wall literary work. Take this line as an example: "Before I built a wall I’d ask to know what hat I was walling in or walling out, And to whom I was like to give offense".
Those last words could be no truer then now. Trump's wall with Mexico is obviously being built with the intent of "walling out" illegals, drugs, and gangs coming in via Mexico. But, there is a cost in that -- like the poem states -- the wall "was like to give offense" to our neighboring country, Mexico.
To me, walls are ugly divisions among societies. A major 1800 mile wall on our southern border would be just that. I would prefer to use existing laws to crack down on employers who attract illegal aliens into the country for employment. We should also change our immigration laws, so that legal, migrant workers can enter. These two changes would greatly reduce work for illegals, and, as we saw during the Great Recession, many returned home due to the lack of jobs. Also, by this point, we should be able to use technology in order to avoid the building of an actual physical wall. Just my opinion.
Source of Graph: http://www.migrationpolicy.org/article/borders-and-walls-do-barriers-deter-unauthorized-migration
Saudi Arabia Constructing 600-Mile Wall To Keep Out ISIS: http://www.newsweek.com/saudi-arabia-constructing-600-mile-long-wall-keep-isis-out-299664
These 14 walls continue to separate the world: https://www.washingtonpost.com/news/worldviews/wp/2014/11/11/these-14-walls-continue-to-separate-the-world/?utm_term=.52efeff1681d
Turkey-Syria border wall completed by half: https://www.dailysabah.com/war-on-terror/2017/02/26/turkey-syria-border-wall-completed-by-half
Robert Frost's 'Mending Wall': https://www.poets.org/poetsorg/poem/mending-wall
More Mexicans Leaving Than Coming to the U.S. | Pew Research: http://www.pewhispanic.org/2015/11/19/more-mexicans-leaving-than-coming-to-the-u-s/