What are 3 walls or other barriers built by countries in the twentieth and twenty first centuries?

Three notable barriers built by countries in the twentieth and twenty-first centuries include the Berlin Wall, which separated East and West Berlin from 1961 until its fall in 1989; the Israeli West Bank barrier, constructed in the early 2000s to separate Israel from Palestinian territories; and the U.S.-Mexico border wall, which has been progressively built and reinforced since the 1990s to deter illegal Immigration. Each of these structures reflects complex political and social issues surrounding borders, security, and national identity.