History has shown since the dawn of civilization that walls work. Whether they have been to protect capital cities, national borders, or entire nations, walls are a proven commodity. Walls are already working in America now. 

The ancient Western Roman Empire survived for hundreds of years thanks to its legal system and military advancements, but in particular its strong security of its borders. Unfortunately for Rome, by the third century A.D., its bureaucracy and policy began to noticeably weaken. The reliance on foreign imports, the greed and vice of Roman bureaucrats, and the self-indulgence of the population all contributed to the empire’s gradual decline.