No continent has been spared from the reinforcement and fortification of borders, which has come to define the beginning of the 21st century. Seventy-four border walls exist across the globe, most erected over the last two decades; at least 15 others were in some stage of planning as of this writing. A large share of these walls, particularly the new ones, are designed to prevent illegal immigration, although they have not proven wholly effective in this regard. But walls can also mark the legacy of wartime defenses, aid the halting of smuggling, and seek to prevent terrorist attacks.
https://www.migrationpolicy.org/article/rapid-proliferation-number-border-walls