If border walls work, please explain how the Mongols conquered China.
If border walls work, please explain how well the Maginot Line worked in WWII
Or how the Benes Line stopped Hitler from invading Czechoslovkia
If border walls work, please explain how well the Siegfried line stopped Patton's 3rd Army
Or how well the Gothic Line saved Mussolini from General Mark Clark.
If walls work, explain why the DeLattre line did not stop the Viet Minh
If walls work, explain how the Egyptians rolled right over the Bar-Lev Line in the Yom Kippur War
If walls work, explain how well the Atlantic Wall stopped D-Day
Or how well the Warta Line worked in Poland in 1939
Or how well the Mannerheim Line working in Finland in 1940
Or how well Offa's Dyke worked at stopping the Vikings
Or how well the Greek Metaxis Line stopped the Germans in 1940
Or how well Hadrian's Wall stopped the Picts and Scots
Or how well the Walls of Byzantium worked stopping the Turks.